Don't make autoconfig/autodiscover subdomains and SRV records when the parent domain has no user accounts

These subdomains/records are for automatic configuration of mail clients, but if there are no user accounts on a domain, there is no need to publish a DNS record, provision a TLS certificate, or create an nginx server config block.

CHANGELOG.md

@@ -9,6 +9,10 @@ Mail:
 * An MTA-STS policy for incoming mail is now published (in DNS and over HTTPS) when the primary hostname and email address domain both have a signed TLS certificate installed.
 * MTA-STS reporting is enabled with reports sent to administrator@ the primary hostname.
 
+DNS:
+
+* autoconfig and autodiscover subdomains and CalDAV/CardDAV SRV records are no longer generated for domains that don't have user accounts since they are unnecessary.
+
 v0.45 (May 16, 2020)
 --------------------
 

management/dns_update.py

@@ -281,18 +281,20 @@ def build_zone(domain, all_domains, additional_records, www_redirect_domains, en
 		if not has_rec(dmarc_qname, "TXT", prefix="v=DMARC1; "):
 			records.append((dmarc_qname, "TXT", 'v=DMARC1; p=reject', "Recommended. Prevents use of this domain name for outbound mail by specifying that the SPF rule should be honoured for mail from @%s." % (qname + "." + domain)))
 
-	# Add CardDAV/CalDAV SRV records on the non-primary hostname that points to the primary hostname.
+	# Add CardDAV/CalDAV SRV records on the non-primary hostname that points to the primary hostname
+	# for autoconfiguration of mail clients (so only domains hosting user accounts need it).
 	# The SRV record format is priority (0, whatever), weight (0, whatever), port, service provider hostname (w/ trailing dot).
-	if domain != env["PRIMARY_HOSTNAME"]:
+	if domain != env["PRIMARY_HOSTNAME"] and domain in get_mail_domains(env, users_only=True):
 		for dav in ("card", "cal"):
 			qname = "_" + dav + "davs._tcp"
 			if not has_rec(qname, "SRV"):
 				records.append((qname, "SRV", "0 0 443 " + env["PRIMARY_HOSTNAME"] + ".", "Recommended. Specifies the hostname of the server that handles CardDAV/CalDAV services for email addresses on this domain."))
 
-	# Adds autoconfiguration A records for all domains.
+	# Adds autoconfiguration A records for all domains that there are user accounts at.
 	# This allows the following clients to automatically configure email addresses in the respective applications.
 	# autodiscover.* - Z-Push ActiveSync Autodiscover
 	# autoconfig.* - Thunderbird Autoconfig
+	if domain in get_mail_domains(env, users_only=True):
 		autodiscover_records = [
 			("autodiscover", "A", env["PUBLIC_IP"], "Provides email configuration autodiscovery support for Z-Push ActiveSync Autodiscover."),
 			("autodiscover", "AAAA", env["PUBLIC_IPV6"], "Provides email configuration autodiscovery support for Z-Push ActiveSync Autodiscover."),

management/mailconfig.py

@@ -258,13 +258,15 @@ def get_domain(emailaddr, as_unicode=True):
 			pass
 	return ret
 
-def get_mail_domains(env, filter_aliases=lambda alias : True):
+def get_mail_domains(env, filter_aliases=lambda alias : True, users_only=False):
 	# Returns the domain names (IDNA-encoded) of all of the email addresses
-	# configured on the system.
-	return set(
-		   [get_domain(login, as_unicode=False) for login in get_mail_users(env)]
-		 + [get_domain(address, as_unicode=False) for address, *_ in get_mail_aliases(env) if filter_aliases(address) ]
-		 )
+	# configured on the system. If users_only is True, only return domains
+	# with email addresses that correspond to user accounts.
+	domains = []
+	domains.extend([get_domain(login, as_unicode=False) for login in get_mail_users(env)])
+	if not users_only:
+		domains.extend([get_domain(address, as_unicode=False) for address, *_ in get_mail_aliases(env) if filter_aliases(address) ])
+	return set(domains)
 
 def add_mail_user(email, pw, privs, env):
 	# validate email

management/web_update.py

@@ -24,13 +24,13 @@ def get_web_domains(env, include_www_redirects=True, exclude_dns_elsewhere=True)
 		# the topmost of each domain we serve.
 		domains |= set('www.' + zone for zone, zonefile in get_dns_zones(env))
 
-	# Add Autoconfiguration domains, allowing us to serve correct SSL certs.
+	# Add Autoconfiguration domains for domains that there are user accounts at:
 	# 'autoconfig.' for Mozilla Thunderbird auto setup.
 	# 'autodiscover.' for Activesync autodiscovery.
-	domains |= set('autoconfig.' + maildomain for maildomain in get_mail_domains(env))
-	domains |= set('autodiscover.' + maildomain for maildomain in get_mail_domains(env))
+	domains |= set('autoconfig.' + maildomain for maildomain in get_mail_domains(env, users_only=True))
+	domains |= set('autodiscover.' + maildomain for maildomain in get_mail_domains(env, users_only=True))
 
-	# 'mta-sts.' for MTA-STS support.
+	# 'mta-sts.' for MTA-STS support for all domains that have email addresses.
 	domains |= set('mta-sts.' + maildomain for maildomain in get_mail_domains(env))
 
 	if exclude_dns_elsewhere: