diff --git a/README.md b/README.md
index 6650221..ec6a55d 100644
--- a/README.md
+++ b/README.md
@@ -80,7 +80,8 @@ notification endpoint set, changes show only on the dashboard; see
       different addresses than on the previous check. A nameserver added or
       removed gets only the NS change notification. When the lookup of a
       nameserver's addresses fails or finds none, its previous addresses are
-      kept and nothing is sent.
+      kept and nothing is sent. The lookup fails when no nameserver it asks
+      answers every one of its queries, for A, AAAA and CNAME.
 - Also watches the domain's own records as a hostname's are watched (see DNS
   Hostname Monitoring below): its A, AAAA, CNAME, MX, TXT, SRV, CAA and NS
   records, stored per nameserver. Their changes are notified as a hostname's
@@ -97,6 +98,19 @@ notification endpoint set, changes show only on the dashboard; see
   its last two labels (a name under `co.uk`, or in a delegated subdomain).
 - Queries **each** authoritative nameserver independently for **all** record
   types: A, AAAA, CNAME, MX, TXT, SRV, CAA, NS.
+- Each record type is a query of its own. When a nameserver answers some types
+  but the query for another gets no usable reply (no reply after two tries, an
+  error reply such as SERVFAIL, a referral, or a reply too large for UDP whose
+  retry over TCP fails), the failure is logged with the reason, and the type is
+  listed in the nameserver's `failedTypes` and keeps the records saved for the
+  nameserver by the previous check. On that check those records are not compared
+  with the other nameservers', so no record change or inconsistency is reported
+  for the type; on the next check they are compared with the nameserver's answer
+  as usual. When the previous check did not know the type's records either,
+  because the nameserver was new or failing then or the type was already listed
+  in `unknownTypes`, the type is also listed in `unknownTypes` and left out of
+  every comparison until it answers. A nameserver none of whose queries got a
+  usable reply has failed (see NS query failure below).
 - Stores results **per nameserver**. The state for a hostname is not a merged
   view — it is a map from nameserver to record set.
 - DNS names inside record values (CNAME, MX, SRV and NS targets) are stored in
@@ -125,8 +139,9 @@ notification endpoint set, changes show only on the dashboard; see
       they keep disagreeing, including after a restart. A nameserver that was
       not in the previous check (newly added, or back after dropping out), or
       failed on it, and answers differently is reported on the check where it
-      answers. If a pair agrees again and later disagrees, the alert is sent
-      again.
+      answers. So is a pair that differs in a record type whose query to either
+      nameserver failed on the previous check. If a pair agrees again and later
+      disagrees, the alert is sent again.
     - **CNAME address change**: The addresses at the end of a name's CNAME chain
       differ from those of the previous check. They are found when its
       nameservers answer with a CNAME and no address; a name that answers with
@@ -545,7 +560,7 @@ reachability:
 
 | Status  | Meaning                                                  |
 | ------- | -------------------------------------------------------- |
-| `ok`    | Query succeeded, records are current                     |
+| `ok`    | Query succeeded, records are current except as below     |
 | `error` | Query failed (timeout, SERVFAIL, REFUSED, network error) |
 
 A nameserver that answers NXDOMAIN or with no records has status `ok` and empty
@@ -554,6 +569,13 @@ nameservers, has status `error`, empty `records`, and the reason in `error`. A
 certificate entry whose TLS connection or handshake failed likewise has status
 `error`, the reason in `error`, and the certificate fields left empty or zero.
 
+A nameserver with status `ok` whose query for one record type failed lists that
+type in `failedTypes` and holds its records from the previous check, which may
+not be current. When the previous check did not know the type's records either,
+because the nameserver was new or failing then or the type was already listed in
+`unknownTypes`, the type is also listed in `unknownTypes`, and `records` holds
+nothing for it. Both lists are left out when empty.
+
 `nameserverAddresses` lists, by nameserver, the sorted addresses its name
 resolves to. A state file without it loads, and the next check fills it in
 without a notification.
@@ -561,10 +583,10 @@ without a notification.
 `cnameAddresses` lists the sorted addresses at the end of the chain of every
 CNAME target a hostname's nameservers gave, found when they answered with a
 CNAME and no address; it is empty when they answered with an address. When a
-chain cannot be followed, or none of the name's nameservers answered, the
-previous check's list is kept, or `null` when no earlier check saved one. A
-state file without it loads, and the first check after that saves it without a
-notification.
+chain cannot be followed, or none of the name's nameservers answered its queries
+for A, AAAA and CNAME, the previous check's list is kept, or `null` when no
+earlier check saved one. A state file without it loads, and the first check
+after that saves it without a notification.
 
 A port entry's `hostnames` lists every name that resolves to its address,
 domains included. A port entry in the older format, with one `hostname` instead
diff --git a/TODO.md b/TODO.md
index 2d97fbb..2895ca3 100644
--- a/TODO.md
+++ b/TODO.md
@@ -19,6 +19,8 @@ trial run of the finished image: https://git.eeqj.de/sneak/dnswatcher/issues/149
 
 # Completed Steps
 
+- 2026-10-02: a record type whose query to a nameserver fails keeps its previous
+  records and alerts nothing; the other types are still saved (closes #231).
 - 2026-10-02: a Port Change notification lists the port's domains on a
   `Domains:` line and its hostnames on a `Hostnames:` line (closes #248).
 - 2026-10-02: the dashboard's Ports table and `/api/v1/status` port entries list
diff --git a/internal/resolver/errors.go b/internal/resolver/errors.go
index f603217..61ca007 100644
--- a/internal/resolver/errors.go
+++ b/internal/resolver/errors.go
@@ -22,6 +22,12 @@ var (
 		"reply is an error or a referral that leads no closer",
 	)
 
+	// ErrTruncated is the reason given for a reply too large for UDP
+	// whose retry over TCP failed.
+	ErrTruncated = errors.New(
+		"reply truncated and its retry over TCP failed",
+	)
+
 	// ErrIntercepted is returned when every root server refused a
 	// query. Root servers refuse no query, so the refusals came from
 	// something on the network answering in their place.
diff --git a/internal/resolver/export_test.go b/internal/resolver/export_test.go
index 07c293b..a0e4103 100644
--- a/internal/resolver/export_test.go
+++ b/internal/resolver/export_test.go
@@ -2,10 +2,21 @@ package resolver
 
 import (
 	"context"
+	"log/slog"
+	"time"
 
 	"github.com/miekg/dns"
 )
 
+// NewWithFailingTCP returns a Resolver whose TCP client gives up before
+// it can connect, so the retry over TCP of every truncated reply fails.
+func NewWithFailingTCP(log *slog.Logger) *Resolver {
+	r := NewFromLogger(log)
+	r.tcp = &tcpClient{timeout: time.Nanosecond}
+
+	return r
+}
+
 // ExtractRecordValue exports extractRecordValue for testing.
 func ExtractRecordValue(rr dns.RR) string {
 	return extractRecordValue(rr)
diff --git a/internal/resolver/iterative.go b/internal/resolver/iterative.go
index 5686622..4b15543 100644
--- a/internal/resolver/iterative.go
+++ b/internal/resolver/iterative.go
@@ -8,6 +8,7 @@ import (
 	"net"
 	"slices"
 	"sort"
+	"strconv"
 	"strings"
 	"time"
 
@@ -99,6 +100,9 @@ func (r *Resolver) tryExchange(
 	return resp, err
 }
 
+// retryTCP returns the reply to msg over TCP when resp, its reply over
+// UDP, is truncated. When that fails it returns resp, still truncated,
+// which holds only the records that fit.
 func (r *Resolver) retryTCP(
 	ctx context.Context,
 	msg *dns.Msg,
@@ -320,13 +324,20 @@ func (r *Resolver) queryServers(
 	return nil, fmt.Errorf("all servers failed: %w", lastErr)
 }
 
+// isErrorReply reports whether msg is an error reply: one with any code
+// but NOERROR and NXDOMAIN, such as SERVFAIL, NOTIMP or FORMERR. An error
+// reply says nothing about the name's records.
+func isErrorReply(msg *dns.Msg) bool {
+	return msg.Rcode != dns.RcodeSuccess && msg.Rcode != dns.RcodeNameError
+}
+
 // usableReply reports whether resp, a reply from one of the servers of
 // zone to a query about name, is usable. An error reply such as SERVFAIL
 // is not. Nor is a referral, unless it refers the query to a zone below
 // zone that name is in: a server that refers it back to zone, up or
 // sideways does not serve zone as it should.
 func usableReply(resp *dns.Msg, zone string, name string) bool {
-	if resp.Rcode != dns.RcodeSuccess && resp.Rcode != dns.RcodeNameError {
+	if isErrorReply(resp) {
 		return false
 	}
 
@@ -714,15 +725,21 @@ func (r *Resolver) queryTypes(
 }
 
 type queryState struct {
-	gotNXDomain bool
-	gotSERVFAIL bool
-	gotRefused  bool
-	gotTimeout  bool
-	gotReferral bool
-	netErr      error
-	hasRecords  bool
+	gotNXDomain   bool
+	gotErrorReply bool
+	errorReply    string // its code, such as SERVFAIL, or number if unnamed
+	gotRefused    bool
+	gotTimeout    bool
+	gotReferral   bool
+	netErr        error
+	hasRecords    bool
+	answered      bool
 }
 
+// queryEachType asks the nameserver at nsIP about hostname once for each
+// record type in qtypes, and lists in resp.FailedTypes the types whose
+// query got no usable reply, logging each with the reason unless ctx was
+// cancelled: shutdown cancels it, and a query it cut short did not fail.
 func (r *Resolver) queryEachType(
 	ctx context.Context,
 	nsIP string,
@@ -737,7 +754,34 @@ func (r *Resolver) queryEachType(
 			break
 		}
 
-		r.querySingleType(ctx, nsIP, hostname, qtype, resp, &state)
+		err := r.querySingleType(ctx, nsIP, hostname, qtype, resp, &state)
+		if err == nil {
+			state.answered = true
+
+			continue
+		}
+
+		rtype := dns.TypeToString[qtype]
+		resp.FailedTypes = append(resp.FailedTypes, rtype)
+
+		if errors.Is(ctx.Err(), context.Canceled) {
+			continue
+		}
+
+		r.log.Warn(
+			"record type query failed",
+			"hostname", hostname,
+			"nameserver", resp.Nameserver,
+			"type", rtype,
+			"error", err,
+		)
+	}
+
+	// The reply about another type can carry the name's CNAME. When the
+	// query for CNAME itself failed, that is left out too, so Records
+	// holds nothing for a failed type.
+	for _, rtype := range resp.FailedTypes {
+		delete(resp.Records, rtype)
 	}
 
 	for k := range resp.Records {
@@ -747,6 +791,9 @@ func (r *Resolver) queryEachType(
 	return state
 }
 
+// querySingleType asks the nameserver at nsIP about hostname's records
+// of type qtype. It returns nil when the nameserver answered: with
+// records, with none, or with NXDOMAIN; otherwise it returns why not.
 func (r *Resolver) querySingleType(
 	ctx context.Context,
 	nsIP string,
@@ -754,7 +801,7 @@ func (r *Resolver) querySingleType(
 	qtype uint16,
 	resp *NameserverResponse,
 	state *queryState,
-) {
+) error {
 	msg, err := r.queryDNS(ctx, nsIP, hostname, qtype)
 	if err != nil {
 		switch {
@@ -766,19 +813,40 @@ func (r *Resolver) querySingleType(
 			state.netErr = err
 		}
 
-		return
+		return err
 	}
 
+	return readReply(msg, resp, state)
+}
+
+// readReply adds to resp the records in msg, a nameserver's reply to a
+// query about one record type. It returns nil when the nameserver
+// answered: with records, with none, or with NXDOMAIN; otherwise it
+// returns why not.
+func readReply(
+	msg *dns.Msg,
+	resp *NameserverResponse,
+	state *queryState,
+) error {
 	if msg.Rcode == dns.RcodeNameError {
 		state.gotNXDomain = true
 
-		return
+		return nil
 	}
 
-	if msg.Rcode == dns.RcodeServerFailure {
-		state.gotSERVFAIL = true
+	if isErrorReply(msg) {
+		state.gotErrorReply = true
 
-		return
+		code, named := dns.RcodeToString[msg.Rcode]
+		if !named {
+			code = strconv.Itoa(msg.Rcode)
+		}
+
+		state.errorReply = code
+
+		return fmt.Errorf(
+			"server returned %s: %w", state.errorReply, ErrUnusableReply,
+		)
 	}
 
 	// A reply with no answer that lists other nameservers, from a server
@@ -791,10 +859,20 @@ func (r *Resolver) querySingleType(
 		len(extractNSSet(msg.Ns)) > 0 {
 		state.gotReferral = true
 
-		return
+		return fmt.Errorf("server returned a referral: %w", ErrUnusableReply)
+	}
+
+	// A reply still truncated is one whose TCP retry failed, and holds
+	// only the records that fit.
+	if msg.Truncated {
+		state.netErr = ErrTruncated
+
+		return ErrTruncated
 	}
 
 	collectAnswerRecords(msg, resp, state)
+
+	return nil
 }
 
 // collectAnswerRecords adds the records in msg's answer to resp, each
@@ -833,23 +911,26 @@ func isTimeout(err error) bool {
 	return false
 }
 
+// classifyResponse sets the nameserver's status. One that answered no
+// record type has failed, and Error says why; one that answered some has
+// the status of those answers.
 func classifyResponse(resp *NameserverResponse, state queryState) {
 	switch {
 	case state.gotNXDomain && !state.hasRecords:
 		resp.Status = StatusNXDomain
-	case state.gotTimeout && !state.hasRecords:
+	case state.gotTimeout && !state.answered:
 		resp.Status = StatusTimeout
 		resp.Error = "all queries timed out"
-	case state.gotSERVFAIL && !state.hasRecords:
+	case state.gotErrorReply && !state.answered:
 		resp.Status = StatusError
-		resp.Error = "server returned SERVFAIL"
-	case state.gotRefused && !state.hasRecords:
+		resp.Error = "server returned " + state.errorReply
+	case state.gotRefused && !state.answered:
 		resp.Status = StatusError
 		resp.Error = "server returned REFUSED"
-	case state.netErr != nil && !state.hasRecords:
+	case state.netErr != nil && !state.answered:
 		resp.Status = StatusError
 		resp.Error = "network error: " + state.netErr.Error()
-	case state.gotReferral && !state.hasRecords:
+	case state.gotReferral && !state.answered:
 		resp.Status = StatusError
 		resp.Error = "server returned a referral"
 	case !state.hasRecords && !state.gotNXDomain:
@@ -1010,9 +1091,11 @@ func (r *Resolver) resolveIPWithCNAME(
 }
 
 // collectIPs returns the addresses in the nameservers' answers and the
-// first CNAME target among them. It returns ErrNoNameserverAnswered when
-// every nameserver timed out, failed or returned a referral: that is not
-// a name with no addresses.
+// first CNAME target among them. A nameserver whose query for one of the
+// types failed gave only part of the addresses, and is left out. It
+// returns ErrNoNameserverAnswered when every nameserver timed out,
+// failed, returned a referral or was left out: that is not a name with
+// no addresses.
 func collectIPs(
 	results map[string]*NameserverResponse,
 ) ([]string, string, error) {
@@ -1025,7 +1108,8 @@ func collectIPs(
 	answered := false
 
 	for _, resp := range results {
-		if resp.Status == StatusTimeout || resp.Status == StatusError {
+		if resp.Status == StatusTimeout || resp.Status == StatusError ||
+			len(resp.FailedTypes) > 0 {
 			continue
 		}
 
diff --git a/internal/resolver/iterative_internal_test.go b/internal/resolver/iterative_internal_test.go
new file mode 100644
index 0000000..f36097d
--- /dev/null
+++ b/internal/resolver/iterative_internal_test.go
@@ -0,0 +1,131 @@
+package resolver
+
+import (
+	"strconv"
+	"syscall"
+	"testing"
+
+	"github.com/miekg/dns"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestClassifyResponse sets a nameserver's status from the results of
+// its queries, built here. One that answered some record types, even
+// with no records, has not failed when its query for another type got
+// no usable reply, whatever the reason; one whose every query got none
+// has.
+func TestClassifyResponse(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name       string
+		results    queryState
+		wantStatus string
+		wantError  string
+	}{
+		{
+			"some types answered with no records, another timed out",
+			queryState{answered: true, gotTimeout: true},
+			StatusNoData, "",
+		},
+		{
+			"some types answered with no records, another got SERVFAIL",
+			queryState{
+				answered: true, gotErrorReply: true, errorReply: "SERVFAIL",
+			},
+			StatusNoData, "",
+		},
+		{
+			"some types answered with no records, another was refused",
+			queryState{answered: true, gotRefused: true},
+			StatusNoData, "",
+		},
+		{
+			"some types answered with no records, another got a network error",
+			queryState{answered: true, netErr: syscall.ECONNREFUSED},
+			StatusNoData, "",
+		},
+		{
+			"some types answered with no records, another's reply was " +
+				"truncated and its retry over TCP failed",
+			queryState{answered: true, netErr: ErrTruncated},
+			StatusNoData, "",
+		},
+		{
+			"some types answered with no records, another got a referral",
+			queryState{answered: true, gotReferral: true},
+			StatusNoData, "",
+		},
+		{
+			"every query timed out",
+			queryState{gotTimeout: true},
+			StatusTimeout, "all queries timed out",
+		},
+		{
+			"every query got NOTIMP",
+			queryState{gotErrorReply: true, errorReply: "NOTIMP"},
+			StatusError, "server returned NOTIMP",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			resp := &NameserverResponse{Status: StatusOK}
+			classifyResponse(resp, tt.results)
+
+			assert.Equal(t, tt.wantStatus, resp.Status)
+			assert.Equal(t, tt.wantError, resp.Error)
+		})
+	}
+}
+
+// TestReadReply checks which replies to a query about one record type,
+// built here, are an answer: one with the code NOERROR or NXDOMAIN. A
+// reply with any other code is not, and the type's query has failed; a
+// nameserver whose only reply it is has failed, and Error gives the
+// code, or its number when the code has no name.
+func TestReadReply(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		rcode      int
+		wantStatus string
+		wantError  string
+	}{
+		{dns.RcodeSuccess, StatusNoData, ""},
+		{dns.RcodeNameError, StatusNXDomain, ""},
+		{dns.RcodeServerFailure, StatusError, "server returned SERVFAIL"},
+		{dns.RcodeNotImplemented, StatusError, "server returned NOTIMP"},
+		{dns.RcodeFormatError, StatusError, "server returned FORMERR"},
+		{12, StatusError, "server returned 12"}, // unassigned, no name
+	}
+
+	for _, tt := range tests {
+		t.Run(strconv.Itoa(tt.rcode), func(t *testing.T) {
+			t.Parallel()
+
+			msg := new(dns.Msg)
+			msg.Authoritative = true
+			msg.Rcode = tt.rcode
+
+			resp := &NameserverResponse{Records: map[string][]string{}}
+
+			var state queryState
+
+			err := readReply(msg, resp, &state)
+			classifyResponse(resp, state)
+
+			if tt.wantStatus == StatusError {
+				require.ErrorIs(t, err, ErrUnusableReply)
+			} else {
+				require.NoError(t, err)
+			}
+
+			assert.Equal(t, tt.wantStatus, resp.Status)
+			assert.Equal(t, tt.wantError, resp.Error)
+		})
+	}
+}
diff --git a/internal/resolver/iterative_test.go b/internal/resolver/iterative_test.go
index ca422cd..836b555 100644
--- a/internal/resolver/iterative_test.go
+++ b/internal/resolver/iterative_test.go
@@ -43,6 +43,25 @@ func TestCollectIPs_FailedIsNoAnswer(t *testing.T) {
 	assert.Empty(t, ips)
 }
 
+// TestCollectIPs_FailedTypeIsNoAnswer checks that a nameserver whose
+// query for one of the types failed is no answer: its addresses are
+// only part of them.
+func TestCollectIPs_FailedTypeIsNoAnswer(t *testing.T) {
+	t.Parallel()
+
+	ips, _, err := resolver.CollectIPs(
+		map[string]*resolver.NameserverResponse{
+			nsExample1: {
+				Records:     map[string][]string{"A": {"192.0.2.1"}},
+				FailedTypes: []string{"AAAA"},
+				Status:      resolver.StatusOK,
+			},
+		},
+	)
+	require.ErrorIs(t, err, resolver.ErrNoNameserverAnswered)
+	assert.Empty(t, ips)
+}
+
 const (
 	// exampleCom is the zone most cases of TestUsableReply and
 	// TestNSSetFrom are about, and wwwExampleCom a name in it.
diff --git a/internal/resolver/resolver.go b/internal/resolver/resolver.go
index 83b3f47..1bdfdb9 100644
--- a/internal/resolver/resolver.go
+++ b/internal/resolver/resolver.go
@@ -31,11 +31,15 @@ type Params struct {
 }
 
 // NameserverResponse holds one nameserver's response for a query.
+// FailedTypes lists the record types whose query got no usable reply,
+// and Records holds nothing for them: their records are not known. When
+// no record type got one, Status and Error say the nameserver failed.
 type NameserverResponse struct {
-	Nameserver string
-	Records    map[string][]string
-	Status     string
-	Error      string
+	Nameserver  string
+	Records     map[string][]string
+	FailedTypes []string
+	Status      string
+	Error       string
 }
 
 // Resolver performs iterative DNS resolution from root servers.
diff --git a/internal/resolver/resolver_test.go b/internal/resolver/resolver_test.go
index ac45b89..94a2fa0 100644
--- a/internal/resolver/resolver_test.go
+++ b/internal/resolver/resolver_test.go
@@ -1,6 +1,7 @@
 package resolver_test
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -366,6 +367,30 @@ func TestQueryNameserver_TXT(t *testing.T) {
 	)
 }
 
+// TestQueryNameserver_TruncatedReplyWhoseTCPRetryFails asks a google.com
+// nameserver about google.com with a resolver whose retries over TCP
+// fail. google.com's TXT records do not fit in a reply over UDP, so TXT
+// is reported as failed, holding none of the records that fit, and
+// logged with the reason, while the nameserver, which answered the other
+// types, is ok.
+func TestQueryNameserver_TruncatedReplyWhoseTCPRetryFails(t *testing.T) {
+	t.Parallel()
+
+	ns := findOneNSForDomain(t, newTestResolver(t), "google.com")
+
+	var logs bytes.Buffer
+
+	r := resolver.NewWithFailingTCP(slog.New(slog.NewTextHandler(&logs, nil)))
+	resp := liveQueryNameserver(t, r, ns, "google.com")
+
+	assert.Equal(t, resolver.StatusOK, resp.Status)
+	assert.Contains(t, resp.FailedTypes, "TXT")
+	assert.NotContains(t, resp.Records, "TXT")
+	assert.Contains(t, logs.String(),
+		"hostname=google.com. nameserver="+ns+" type=TXT error=",
+	)
+}
+
 func TestQueryNameserver_NXDomain(t *testing.T) {
 	t.Parallel()
 
@@ -1001,6 +1026,29 @@ func TestQueryNameserverIP_Timeout(t *testing.T) {
 	assert.NotEmpty(t, resp.Error)
 }
 
+// TestQueryNameserverIP_CancelledLogsNothing cancels the context while
+// a query to 192.0.2.1, where nothing answers, is waiting for a reply,
+// as shutdown does. The query was cut short, not failed, so nothing is
+// logged.
+func TestQueryNameserverIP_CancelledLogsNothing(t *testing.T) {
+	t.Parallel()
+
+	var logs bytes.Buffer
+
+	r := resolver.NewFromLogger(slog.New(slog.NewTextHandler(&logs, nil)))
+
+	ctx, cancel := context.WithCancel(context.Background())
+	t.Cleanup(cancel)
+	time.AfterFunc(100*time.Millisecond, cancel)
+
+	_, err := r.QueryNameserverIP(
+		ctx, "unreachable.test.", "192.0.2.1", "example.com",
+	)
+	require.NoError(t, err)
+
+	assert.Empty(t, logs.String())
+}
+
 // TestCollectIPs_NoNameserverAnswered takes the response of a
 // nameserver at 192.0.2.1, where nothing answers, as
 // TestQueryNameserverIP_Timeout does. Addresses collected from
diff --git a/internal/state/state.go b/internal/state/state.go
index 4f5a325..eecca4e 100644
--- a/internal/state/state.go
+++ b/internal/state/state.go
@@ -46,11 +46,18 @@ type DomainState struct {
 }
 
 // NameserverRecordState holds one NS's response for a hostname.
+// FailedTypes lists the record types whose query to the nameserver
+// failed on this check: Records holds for them the records saved by the
+// previous check, which are kept. UnknownTypes lists those of them whose
+// records the previous check did not know either, as when the
+// nameserver was new or failing then: Records holds nothing for them.
 type NameserverRecordState struct {
-	Records     map[string][]string `json:"records"`
-	Status      string              `json:"status"`
-	Error       string              `json:"error,omitempty"`
-	LastChecked time.Time           `json:"lastChecked"`
+	Records      map[string][]string `json:"records"`
+	FailedTypes  []string            `json:"failedTypes,omitempty"`
+	UnknownTypes []string            `json:"unknownTypes,omitempty"`
+	Status       string              `json:"status"`
+	Error        string              `json:"error,omitempty"`
+	LastChecked  time.Time           `json:"lastChecked"`
 }
 
 // HostnameState holds per-nameserver monitoring state for a hostname.
diff --git a/internal/state/state_test.go b/internal/state/state_test.go
index b2f7391..e511014 100644
--- a/internal/state/state_test.go
+++ b/internal/state/state_test.go
@@ -236,6 +236,61 @@ func TestSaveLoadRoundTrip_CNAMEAddresses(t *testing.T) {
 	}
 }
 
+// TestSaveLoadRoundTrip_FailedTypes checks that a nameserver's
+// failedTypes and unknownTypes survive a save and load. Without
+// unknownTypes, a type whose records were not known would load as one
+// with no records.
+func TestSaveLoadRoundTrip_FailedTypes(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+	s := state.NewForTestWithDataDir(dir)
+
+	failed := []string{"TXT", "CAA"}
+	unknown := []string{"CAA"}
+
+	s.SetHostnameState(testHostname, &state.HostnameState{
+		RecordsByNameserver: map[string]*state.NameserverRecordState{
+			testNS1: {
+				Records:      map[string][]string{"TXT": {"v=spf1 -all"}},
+				FailedTypes:  failed,
+				UnknownTypes: unknown,
+				Status:       "ok",
+			},
+		},
+	})
+
+	err := s.Save()
+	if err != nil {
+		t.Fatalf("Save() error: %v", err)
+	}
+
+	loaded := state.NewForTestWithDataDir(dir)
+
+	err = loaded.Load()
+	if err != nil {
+		t.Fatalf("Load() error: %v", err)
+	}
+
+	hs, ok := loaded.GetHostnameState(testHostname)
+	if !ok {
+		t.Fatal("missing hostname " + testHostname)
+	}
+
+	ns1 := hs.RecordsByNameserver[testNS1]
+	if ns1 == nil {
+		t.Fatal("missing nameserver " + testNS1)
+	}
+
+	if !reflect.DeepEqual(ns1.FailedTypes, failed) {
+		t.Errorf("failedTypes: got %#v", ns1.FailedTypes)
+	}
+
+	if !reflect.DeepEqual(ns1.UnknownTypes, unknown) {
+		t.Errorf("unknownTypes: got %#v", ns1.UnknownTypes)
+	}
+}
+
 // TestLoadStateFromBeforeCNAMEAddresses loads a state file written
 // before the addresses at the end of a hostname's CNAME chain were
 // saved. They load as not known (nil), not as none.
diff --git a/internal/watcher/cname_test.go b/internal/watcher/cname_test.go
index b3c549f..9f492f1 100644
--- a/internal/watcher/cname_test.go
+++ b/internal/watcher/cname_test.go
@@ -202,6 +202,42 @@ func TestCNAMEWhoseNameserversAllFailedKeepsPrevious(t *testing.T) {
 	}
 }
 
+// TestCNAMEWhoseAddressQueryFailedKeepsPrevious checks a name whose
+// nameserver answered, but whose query for A, AAAA or CNAME failed with
+// nothing kept for it. That is not an answer with no address: the
+// addresses the previous check saved from following its CNAME are kept,
+// and nothing is looked up, the watcher having no resolver.
+func TestCNAMEWhoseAddressQueryFailedKeepsPrevious(t *testing.T) {
+	t.Parallel()
+
+	for _, rtype := range []string{"A", "AAAA", "CNAME"} {
+		t.Run(rtype, func(t *testing.T) {
+			t.Parallel()
+
+			w := watcher.NewForTest(nil, nil, nil, nil, nil, nil)
+
+			current := saved(map[string]*state.NameserverRecordState{
+				nsA: {
+					Records:      map[string][]string{},
+					FailedTypes:  []string{rtype},
+					UnknownTypes: []string{rtype},
+					Status:       "ok",
+				},
+			})
+			prev := cnameState(oldIP)
+
+			w.ResolveCNAMEAddresses(t.Context(), host, current, prev)
+
+			if !slices.Equal(current.CNAMEAddresses, prev.CNAMEAddresses) {
+				t.Errorf(
+					"saved %v, want %v",
+					current.CNAMEAddresses, prev.CNAMEAddresses,
+				)
+			}
+		})
+	}
+}
+
 // cnameTo builds the records of a nameserver that answered with a CNAME
 // to target and no address.
 func cnameTo(target string) map[string][]string {
diff --git a/internal/watcher/export_test.go b/internal/watcher/export_test.go
index e932a2c..e527a2d 100644
--- a/internal/watcher/export_test.go
+++ b/internal/watcher/export_test.go
@@ -120,7 +120,8 @@ func (w *Watcher) RunTLSChecks(ctx context.Context) {
 // BuildHostnameState exports buildHostnameState for testing.
 func BuildHostnameState(
 	results map[string]*resolver.NameserverResponse,
+	prev *state.HostnameState,
 	now time.Time,
 ) *state.HostnameState {
-	return buildHostnameState(results, now)
+	return buildHostnameState(results, prev, now)
 }
diff --git a/internal/watcher/failedtype_test.go b/internal/watcher/failedtype_test.go
new file mode 100644
index 0000000..832ebf2
--- /dev/null
+++ b/internal/watcher/failedtype_test.go
@@ -0,0 +1,364 @@
+package watcher_test
+
+import (
+	"maps"
+	"slices"
+	"testing"
+	"time"
+
+	"sneak.berlin/go/dnswatcher/internal/resolver"
+	"sneak.berlin/go/dnswatcher/internal/state"
+	"sneak.berlin/go/dnswatcher/internal/watcher"
+)
+
+const (
+	// txt is the record type whose query fails in these tests.
+	txt  = "TXT"
+	spf1 = "v=spf1 -all"
+	spf2 = "v=spf1 include:example.net -all"
+)
+
+// response is a nameserver's response with these records, whose queries
+// for failedTypes failed.
+func response(
+	records map[string][]string,
+	failedTypes ...string,
+) *resolver.NameserverResponse {
+	return &resolver.NameserverResponse{
+		Records:     records,
+		FailedTypes: failedTypes,
+		Status:      resolver.StatusOK,
+	}
+}
+
+// savedChecks saves the state of each check in turn from the
+// nameservers' responses, each from the state the check before saved.
+func savedChecks(
+	checks ...map[string]*resolver.NameserverResponse,
+) []*state.HostnameState {
+	states := make([]*state.HostnameState, 0, len(checks))
+
+	var prev *state.HostnameState
+
+	for _, results := range checks {
+		prev = watcher.BuildHostnameState(results, prev, time.Now())
+		states = append(states, prev)
+	}
+
+	return states
+}
+
+// TestFailedTypeKeepsPreviousRecords saves a check in which nsA's query
+// for TXT failed, after previous checks of several kinds. TXT is always
+// saved in FailedTypes, and in UnknownTypes when there was nothing to
+// keep.
+func TestFailedTypeKeepsPreviousRecords(t *testing.T) {
+	t.Parallel()
+
+	aOnly := map[string][]string{"A": {ip1}}
+	withTXT := map[string][]string{"A": {ip1}, txt: {spf1}}
+	txtKept := &state.NameserverRecordState{
+		Records: withTXT, FailedTypes: []string{txt}, Status: "ok",
+	}
+	txtNotKnown := &state.NameserverRecordState{
+		Records:      aOnly,
+		FailedTypes:  []string{txt},
+		UnknownTypes: []string{txt},
+		Status:       "ok",
+	}
+
+	tests := []struct {
+		name        string
+		prev        *state.HostnameState
+		wantRecords map[string][]string
+		wantUnknown []string
+	}{
+		{
+			"previous TXT records are kept",
+			saved(map[string]*state.NameserverRecordState{nsA: answered(withTXT)}),
+			withTXT, nil,
+		},
+		{
+			"previous check had no TXT records",
+			saved(map[string]*state.NameserverRecordState{nsA: answered(aOnly)}),
+			aOnly, nil,
+		},
+		{
+			"TXT failed on the previous check, which kept its records",
+			saved(map[string]*state.NameserverRecordState{nsA: txtKept}),
+			withTXT, nil,
+		},
+		{"first check", nil, aOnly, []string{txt}},
+		{
+			"nameserver new on this check",
+			saved(map[string]*state.NameserverRecordState{nsB: answered(withTXT)}),
+			aOnly, []string{txt},
+		},
+		{
+			"nameserver failed on the previous check",
+			saved(map[string]*state.NameserverRecordState{nsA: failed()}),
+			aOnly, []string{txt},
+		},
+		{
+			"TXT failed on the previous check with nothing to keep",
+			saved(map[string]*state.NameserverRecordState{nsA: txtNotKnown}),
+			aOnly, []string{txt},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			hs := watcher.BuildHostnameState(
+				map[string]*resolver.NameserverResponse{
+					nsA: response(map[string][]string{"A": {ip1}}, txt),
+				},
+				tt.prev, time.Now(),
+			)
+
+			got := hs.RecordsByNameserver[nsA]
+			if got.Status != "ok" ||
+				!maps.EqualFunc(got.Records, tt.wantRecords, slices.Equal) ||
+				!slices.Equal(got.FailedTypes, []string{txt}) ||
+				!slices.Equal(got.UnknownTypes, tt.wantUnknown) {
+				t.Errorf(
+					"saved status %q, records %v, failed types %v, "+
+						"unknown types %v; want ok, %v, [%s], %v",
+					got.Status, got.Records, got.FailedTypes,
+					got.UnknownTypes, tt.wantRecords, txt, tt.wantUnknown,
+				)
+			}
+		})
+	}
+}
+
+// TestFailedTypeAlerts saves the checks of each case in turn from the
+// nameservers' responses, the first being the state loaded at startup,
+// and counts the alerts sent. nsB's TXT query fails on one check, and
+// nothing changes.
+func TestFailedTypeAlerts(t *testing.T) {
+	t.Parallel()
+
+	records := map[string][]string{"A": {ip1}, txt: {spf1}}
+	aOnly := map[string][]string{"A": {ip1}}
+
+	bothAnswer := map[string]*resolver.NameserverResponse{
+		nsA: response(records), nsB: response(records),
+	}
+	bTXTFails := map[string]*resolver.NameserverResponse{
+		nsA: response(records), nsB: response(aOnly, txt),
+	}
+	onlyA := map[string]*resolver.NameserverResponse{
+		nsA: response(records),
+	}
+	bFails := map[string]*resolver.NameserverResponse{
+		nsA: response(records),
+		nsB: {
+			Records: map[string][]string{},
+			Status:  resolver.StatusTimeout,
+			Error:   "all queries timed out",
+		},
+	}
+
+	tests := []struct {
+		name   string
+		checks []map[string]*resolver.NameserverResponse
+		want   alertCounts
+	}{
+		{
+			"type failing at one nameserver alerts nothing, nor its next answer",
+			[]map[string]*resolver.NameserverResponse{
+				bothAnswer, bTXTFails, bothAnswer,
+			},
+			alertCounts{},
+		},
+		{
+			"type failing on the first check alerts nothing on the next",
+			[]map[string]*resolver.NameserverResponse{bTXTFails, bothAnswer},
+			alertCounts{},
+		},
+		{
+			"type failing at a nameserver new on that check alerts nothing",
+			[]map[string]*resolver.NameserverResponse{
+				onlyA, bTXTFails, bothAnswer,
+			},
+			alertCounts{},
+		},
+		{
+			"type failing at a recovering nameserver alerts the recovery",
+			[]map[string]*resolver.NameserverResponse{
+				bFails, bTXTFails, bothAnswer,
+			},
+			alertCounts{recoveries: 1},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			states := savedChecks(tt.checks...)
+
+			got := countAlerts(t, states[0], states[1:])
+			if got != tt.want {
+				t.Errorf("sent %+v, want %+v", got, tt.want)
+			}
+		})
+	}
+}
+
+// TestFailedTypeComparedOnceItAnswers saves the checks of each case in
+// turn as TestFailedTypeAlerts does. nsB's TXT query fails on one check,
+// and the TXT record changes: the change is sent as a Record Change for
+// each nameserver on the check where it answers it, and an Inconsistency
+// only when nsB still answers the old record.
+func TestFailedTypeComparedOnceItAnswers(t *testing.T) {
+	t.Parallel()
+
+	records := map[string][]string{"A": {ip1}, txt: {spf1}}
+	changed := map[string][]string{"A": {ip1}, txt: {spf2}}
+	aOnly := map[string][]string{"A": {ip1}}
+
+	bothAnswer := map[string]*resolver.NameserverResponse{
+		nsA: response(records), nsB: response(records),
+	}
+	bTXTFails := map[string]*resolver.NameserverResponse{
+		nsA: response(records), nsB: response(aOnly, txt),
+	}
+	bothChange := map[string]*resolver.NameserverResponse{
+		nsA: response(changed), nsB: response(changed),
+	}
+	aChangesBTXTFails := map[string]*resolver.NameserverResponse{
+		nsA: response(changed), nsB: response(aOnly, txt),
+	}
+	bStillOld := map[string]*resolver.NameserverResponse{
+		nsA: response(changed), nsB: response(records),
+	}
+
+	tests := []struct {
+		name   string
+		checks []map[string]*resolver.NameserverResponse
+		want   alertCounts
+	}{
+		{
+			"change made while the type failed",
+			[]map[string]*resolver.NameserverResponse{
+				bothAnswer, bTXTFails, bothChange,
+			},
+			alertCounts{recordChanges: 2},
+		},
+		{
+			"change seen at one nameserver while the other's type failed",
+			[]map[string]*resolver.NameserverResponse{
+				bothAnswer, aChangesBTXTFails, bothChange,
+			},
+			alertCounts{recordChanges: 2},
+		},
+		{
+			"old record answered after the type failed",
+			[]map[string]*resolver.NameserverResponse{
+				bothAnswer, aChangesBTXTFails, bStillOld,
+			},
+			alertCounts{recordChanges: 1, inconsistencies: 1},
+		},
+		{
+			"change after the type failed on the first check and answered",
+			[]map[string]*resolver.NameserverResponse{
+				bTXTFails, bothAnswer, bothChange,
+			},
+			alertCounts{recordChanges: 2},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			states := savedChecks(tt.checks...)
+
+			got := countAlerts(t, states[0], states[1:])
+			if got != tt.want {
+				t.Errorf("sent %+v, want %+v", got, tt.want)
+			}
+		})
+	}
+}
+
+// TestFailedTypeLeftOutOfMessages checks that a Record Change and an
+// Inconsistency name only the record types they compared. nsB's TXT
+// records are not known on the first check, and on the second either
+// answered or still not known; nsB's A record changes, so both alerts
+// are sent and name the A record alone.
+func TestFailedTypeLeftOutOfMessages(t *testing.T) {
+	t.Parallel()
+
+	withTXT := map[string][]string{"A": {ip1}, txt: {spf1}}
+	txtNotKnown := func(address string) *state.NameserverRecordState {
+		return &state.NameserverRecordState{
+			Records:      map[string][]string{"A": {address}},
+			FailedTypes:  []string{txt},
+			UnknownTypes: []string{txt},
+			Status:       "ok",
+		}
+	}
+
+	before := saved(map[string]*state.NameserverRecordState{
+		nsA: answered(withTXT), nsB: txtNotKnown(ip1),
+	})
+
+	tests := []struct {
+		name  string
+		after *state.HostnameState
+	}{
+		{
+			"TXT answers",
+			saved(map[string]*state.NameserverRecordState{
+				nsA: answered(withTXT),
+				nsB: answered(map[string][]string{"A": {ip2}, txt: {spf1}}),
+			}),
+		},
+		{
+			"TXT still not known",
+			saved(map[string]*state.NameserverRecordState{
+				nsA: answered(withTXT), nsB: txtNotKnown(ip2),
+			}),
+		},
+	}
+
+	want := map[string]string{
+		"Record Change: " + host: "Hostname: " + host +
+			"\nNameserver: " + nsB + "\nType: A\nOld: " + ip1 + "\nNew: " + ip2,
+		"Inconsistency: " + host: "Hostname: " + host +
+			"\nType: A\n" + nsA + ": " + ip1 + "\n" + nsB + ": " + ip2,
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			// The hostname change detection uses only the notifier.
+			notifier := &mockNotifier{}
+			w := watcher.NewForTest(nil, nil, nil, nil, nil, notifier)
+
+			w.DetectHostnameChanges(t.Context(), host, before, tt.after)
+
+			notifications := notifier.getNotifications()
+			if len(notifications) != len(want) {
+				t.Fatalf(
+					"sent %d notifications, want %d: %v",
+					len(notifications), len(want), notifications,
+				)
+			}
+
+			for _, n := range notifications {
+				if n.Message != want[n.Title] {
+					t.Errorf(
+						"%s message:\n%s\nwant:\n%s",
+						n.Title, n.Message, want[n.Title],
+					)
+				}
+			}
+		})
+	}
+}
diff --git a/internal/watcher/nsfailure_test.go b/internal/watcher/nsfailure_test.go
index afae908..e9147c1 100644
--- a/internal/watcher/nsfailure_test.go
+++ b/internal/watcher/nsfailure_test.go
@@ -201,7 +201,7 @@ func TestNameserverThatNeverAnswers(t *testing.T) {
 	}
 
 	hs := watcher.BuildHostnameState(
-		map[string]*resolver.NameserverResponse{nsA: resp}, time.Now(),
+		map[string]*resolver.NameserverResponse{nsA: resp}, nil, time.Now(),
 	)
 
 	got := hs.RecordsByNameserver[nsA]
@@ -256,7 +256,7 @@ func TestNameserverThatAnswersNXDOMAIN(t *testing.T) {
 	}
 
 	hs := watcher.BuildHostnameState(
-		map[string]*resolver.NameserverResponse{ns: resp}, time.Now(),
+		map[string]*resolver.NameserverResponse{ns: resp}, nil, time.Now(),
 	)
 
 	got := hs.RecordsByNameserver[ns]
@@ -320,7 +320,7 @@ func TestNameserverThatRefuses(t *testing.T) {
 	}
 
 	hs := watcher.BuildHostnameState(
-		map[string]*resolver.NameserverResponse{ns: resp}, time.Now(),
+		map[string]*resolver.NameserverResponse{ns: resp}, nil, time.Now(),
 	)
 
 	got := hs.RecordsByNameserver[ns]
diff --git a/internal/watcher/watcher.go b/internal/watcher/watcher.go
index 0a09014..5649e92 100644
--- a/internal/watcher/watcher.go
+++ b/internal/watcher/watcher.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"log/slog"
+	"maps"
 	"slices"
 	"sort"
 	"strings"
@@ -401,8 +402,10 @@ func (w *Watcher) checkHostname(
 		return
 	}
 
+	prev, _ := w.state.GetHostnameState(hostname)
+
 	w.updateHostnameState(
-		ctx, hostname, buildHostnameState(results, time.Now().UTC()),
+		ctx, hostname, buildHostnameState(results, prev, time.Now().UTC()),
 	)
 }
 
@@ -432,8 +435,9 @@ func (w *Watcher) updateHostnameState(
 // the addresses found for all of them are saved, so nameservers that
 // disagree on the target do not change the result from check to check.
 // The addresses saved in prev, which may be nil, are kept when none of
-// the name's nameservers answered, and when a target cannot be
-// followed, as when no nameserver of a zone in its chain answers.
+// the name's nameservers answered its queries for A, AAAA and CNAME,
+// and when a target cannot be followed, as when no nameserver of a zone
+// in its chain answers.
 func (w *Watcher) resolveCNAMEAddresses(
 	ctx context.Context,
 	hostname string,
@@ -451,7 +455,10 @@ func (w *Watcher) resolveCNAMEAddresses(
 	targets := make(map[string]bool)
 
 	for _, nsState := range current.RecordsByNameserver {
-		if nsState.Status != statusOK {
+		if nsState.Status != statusOK ||
+			slices.Contains(nsState.FailedTypes, "A") ||
+			slices.Contains(nsState.FailedTypes, "AAAA") ||
+			slices.Contains(nsState.FailedTypes, "CNAME") {
 			continue
 		}
 
@@ -497,11 +504,13 @@ func (w *Watcher) resolveCNAMEAddresses(
 }
 
 // buildHostnameState saves each nameserver's response. A nameserver
-// that answered, even with NXDOMAIN or no records, is saved as ok; one
-// that timed out or failed is saved as error with the reason, and its
-// empty record set is not an answer.
+// that answered, even with NXDOMAIN or no records, is saved as ok, with
+// the record types whose query failed; one that timed out or failed is
+// saved as error with the reason, and its empty record set is not an
+// answer. prev is the hostname's state from the previous check, or nil.
 func buildHostnameState(
 	results map[string]*resolver.NameserverResponse,
+	prev *state.HostnameState,
 	now time.Time,
 ) *state.HostnameState {
 	hs := &state.HostnameState{
@@ -513,7 +522,7 @@ func buildHostnameState(
 
 	for ns, resp := range results {
 		nsState := &state.NameserverRecordState{
-			Records:     resp.Records,
+			Records:     maps.Clone(resp.Records),
 			Status:      statusOK,
 			LastChecked: now,
 		}
@@ -522,6 +531,15 @@ func buildHostnameState(
 			resp.Status == resolver.StatusError {
 			nsState.Status = statusError
 			nsState.Error = resp.Error
+		} else {
+			nsState.FailedTypes = resp.FailedTypes
+
+			var prevNS *state.NameserverRecordState
+			if prev != nil {
+				prevNS = prev.RecordsByNameserver[ns]
+			}
+
+			keepFailedTypes(nsState, prevNS)
 		}
 
 		hs.RecordsByNameserver[ns] = nsState
@@ -530,6 +548,27 @@ func buildHostnameState(
 	return hs
 }
 
+// keepFailedTypes copies into nsState, for each record type in its
+// FailedTypes, the records prevNS, the nameserver's state from the
+// previous check, holds for that type, which may be none. When prevNS
+// does not know them either, because the nameserver was new or failing
+// then or the type was in its UnknownTypes, the type goes in
+// nsState.UnknownTypes instead.
+func keepFailedTypes(nsState, prevNS *state.NameserverRecordState) {
+	for _, rtype := range nsState.FailedTypes {
+		if prevNS == nil || prevNS.Status != statusOK ||
+			slices.Contains(prevNS.UnknownTypes, rtype) {
+			nsState.UnknownTypes = append(nsState.UnknownTypes, rtype)
+
+			continue
+		}
+
+		if records, ok := prevNS.Records[rtype]; ok {
+			nsState.Records[rtype] = records
+		}
+	}
+}
+
 func (w *Watcher) detectHostnameChanges(
 	ctx context.Context,
 	hostname string,
@@ -618,7 +657,10 @@ func (w *Watcher) detectCNAMEAddressChanges(
 
 // detectRecordChanges compares each nameserver's records with those of
 // the previous check. Only answers are compared: a nameserver that
-// failed on either check has no records to compare.
+// failed on either check has no records to compare. The records kept
+// for a record type whose query failed are compared too, but not those
+// of a type in UnknownTypes on either check, which the message leaves
+// out as well.
 func (w *Watcher) detectRecordChanges(
 	ctx context.Context,
 	hostname string,
@@ -630,7 +672,11 @@ func (w *Watcher) detectRecordChanges(
 			continue
 		}
 
-		if recordsEqual(prevNS.Records, cur.Records) {
+		unknown := slices.Concat(prevNS.UnknownTypes, cur.UnknownTypes)
+		oldRecords := withoutTypes(prevNS.Records, unknown)
+		newRecords := withoutTypes(cur.Records, unknown)
+
+		if recordsEqual(oldRecords, newRecords) {
 			continue
 		}
 
@@ -638,8 +684,8 @@ func (w *Watcher) detectRecordChanges(
 			"%s\nNameserver: %s\n%s",
 			w.nameLine(hostname), ns,
 			recordDifferences(
-				"Old", prevNS.Records,
-				"New", cur.Records,
+				"Old", oldRecords,
+				"New", newRecords,
 			),
 		)
 
@@ -726,13 +772,19 @@ func (w *Watcher) detectInconsistencies(
 ) {
 	for _, pair := range newlyDisagreeingPairs(prev, current) {
 		ns1, ns2 := pair[0], pair[1]
+		state1 := current.RecordsByNameserver[ns1]
+		state2 := current.RecordsByNameserver[ns2]
+
+		// The record types left out of the comparison are left out of
+		// the message too.
+		failed := slices.Concat(state1.FailedTypes, state2.FailedTypes)
 
 		msg := fmt.Sprintf(
 			"%s\n%s",
 			w.nameLine(hostname),
 			recordDifferences(
-				ns1, current.RecordsByNameserver[ns1].Records,
-				ns2, current.RecordsByNameserver[ns2].Records,
+				ns1, withoutTypes(state1.Records, failed),
+				ns2, withoutTypes(state2.Records, failed),
 			),
 		)
 
@@ -750,7 +802,9 @@ func (w *Watcher) detectInconsistencies(
 // except pairs where both nameservers answered in prev and already
 // differed there. A nameserver missing from prev, or that failed there,
 // is paired with every nameserver it differs from. A nameserver that
-// failed in current has no records to compare and is in no pair.
+// failed in current has no records to compare and is in no pair. In
+// both checks, a record type whose query failed at either nameserver is
+// not compared.
 func newlyDisagreeingPairs(
 	prev, current *state.HostnameState,
 ) [][2]string {
@@ -767,9 +821,9 @@ func newlyDisagreeingPairs(
 
 	for i, ns1 := range nameservers {
 		for _, ns2 := range nameservers[i+1:] {
-			if recordsEqual(
-				current.RecordsByNameserver[ns1].Records,
-				current.RecordsByNameserver[ns2].Records,
+			if nameserversAgree(
+				current.RecordsByNameserver[ns1],
+				current.RecordsByNameserver[ns2],
 			) {
 				continue
 			}
@@ -779,7 +833,7 @@ func newlyDisagreeingPairs(
 
 			if ok1 && ok2 &&
 				prev1.Status == statusOK && prev2.Status == statusOK &&
-				!recordsEqual(prev1.Records, prev2.Records) {
+				!nameserversAgree(prev1, prev2) {
 				continue
 			}
 
@@ -1268,6 +1322,33 @@ func toSet(items []string) map[string]bool {
 	return set
 }
 
+// nameserversAgree reports whether two nameservers' states from the same
+// check hold the same records, leaving out the record types either lists
+// in FailedTypes: the records held for those are kept from an earlier
+// check, or not known.
+func nameserversAgree(a, b *state.NameserverRecordState) bool {
+	failed := slices.Concat(a.FailedTypes, b.FailedTypes)
+
+	return recordsEqual(
+		withoutTypes(a.Records, failed), withoutTypes(b.Records, failed),
+	)
+}
+
+// withoutTypes returns a copy of records without the record types in
+// types.
+func withoutTypes(
+	records map[string][]string,
+	types []string,
+) map[string][]string {
+	records = maps.Clone(records)
+
+	for _, rtype := range types {
+		delete(records, rtype)
+	}
+
+	return records
+}
+
 func recordsEqual(
 	a, b map[string][]string,
 ) bool {