175 lines
8.2 KiB
Bash
Executable File
175 lines
8.2 KiB
Bash
Executable File
#!/bin/bash
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#
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# Postfix (SMTP)
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# --------------
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#
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# Postfix handles the transmission of email between servers
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# using the SMTP protocol. It is a Mail Transfer Agent (MTA).
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#
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# Postfix listens on port 25 (SMTP) for incoming mail from
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# other servers on the Internet. It is responsible for very
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# basic email filtering such as by IP address and greylisting,
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# it checks that the destination address is valid, rewrites
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# destinations according to aliases, and passses email on to
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# another service for local mail delivery.
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#
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# The first hop in local mail delivery is to Spamassassin via
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# LMTP. Spamassassin then passes mail over to Dovecot for
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# storage in the user's mailbox.
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#
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# Postfix also listens on port 587 (SMTP+STARTLS) for
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# connections from users who can authenticate and then sends
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# their email out to the outside world. Postfix queries Dovecot
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# to authenticate users.
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#
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# Address validation, alias rewriting, and user authentication
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# is configured in a separate setup script mail-users.sh
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# because of the overlap of this part with the Dovecot
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# configuration.
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source setup/functions.sh # load our functions
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source /etc/mailinabox.conf # load global vars
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# ### Install packages.
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# Install postfix's packages.
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#
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# * `postfix`: The SMTP server.
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# * `postfix-pcre`: Enables header filtering.
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# * `postgrey`: A mail policy service that soft-rejects mail the first time
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# it is received. Spammers don't usually try agian. Legitimate mail
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# always will.
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# * `ca-certificates`: A trust store used to squelch postfix warnings about
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# untrusted opportunistically-encrypted connections.
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apt_install postfix postfix-pcre postgrey ca-certificates
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# ### Basic Settings
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# Set some basic settings...
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#
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# * Have postfix listen on all network interfaces.
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# * Set our name (the Debian default seems to be "localhost" but make it our hostname).
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# * Set the name of the local machine to localhost, which means xxx@localhost is delivered locally, although we don't use it.
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# * Set the SMTP banner (which must have the hostname first, then anything).
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tools/editconf.py /etc/postfix/main.cf \
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inet_interfaces=all \
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myhostname=$PRIMARY_HOSTNAME\
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smtpd_banner="\$myhostname ESMTP Hi, I'm a Mail-in-a-Box (Ubuntu/Postfix; see https://mailinabox.email/)" \
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mydestination=localhost
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# ### Outgoing Mail
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# Enable the 'submission' port 587 smtpd server and tweak its settings.
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#
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# * Require the best ciphers for incoming connections per http://baldric.net/2013/12/07/tls-ciphers-in-postfix-and-dovecot/.
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# By putting this setting here we leave opportunistic TLS on incoming mail at default cipher settings (any cipher is better than none).
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# * Give it a different name in syslog to distinguish it from the port 25 smtpd server.
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# * Add a new cleanup service specific to the submission service ('authclean')
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# that filters out privacy-sensitive headers on mail being sent out by
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# authenticated users.
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tools/editconf.py /etc/postfix/master.cf -s -w \
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"submission=inet n - - - - smtpd
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-o syslog_name=postfix/submission
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-o smtpd_tls_ciphers=high -o smtpd_tls_protocols=!SSLv2,!SSLv3
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-o cleanup_service_name=authclean" \
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"authclean=unix n - - - 0 cleanup
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-o header_checks=pcre:/etc/postfix/outgoing_mail_header_filters"
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# Install the `outgoing_mail_header_filters` file required by the new 'authclean' service.
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cp conf/postfix_outgoing_mail_header_filters /etc/postfix/outgoing_mail_header_filters
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# Enable TLS on these and all other connections (i.e. ports 25 *and* 587) and
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# require TLS before a user is allowed to authenticate. This also makes
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# opportunistic TLS available on *incoming* mail.
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# Set stronger DH parameters, which via openssl tend to default to 1024 bits
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# (see ssl.sh).
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tools/editconf.py /etc/postfix/main.cf \
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smtpd_tls_security_level=may\
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smtpd_tls_auth_only=yes \
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smtpd_tls_cert_file=$STORAGE_ROOT/ssl/ssl_certificate.pem \
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smtpd_tls_key_file=$STORAGE_ROOT/ssl/ssl_private_key.pem \
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smtpd_tls_dh1024_param_file=$STORAGE_ROOT/ssl/dh2048.pem \
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smtpd_tls_received_header=yes
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# Prevent non-authenticated users from sending mail that requires being
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# relayed elsewhere. We don't want to be an "open relay". On outbound
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# mail, require one of:
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#
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# * `permit_sasl_authenticated`: Authenticated users (i.e. on port 587).
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# * `permit_mynetworks`: Mail that originates locally.
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# * `reject_unauth_destination`: No one else. (Permits mail whose destination is local and rejects other mail.)
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tools/editconf.py /etc/postfix/main.cf \
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smtpd_relay_restrictions=permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination
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# ### DANE
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# When connecting to remote SMTP servers, prefer TLS and use DANE if available.
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#
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# Prefering ("opportunistic") TLS means Postfix will use TLS if the remote end
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# offers it, otherwise it will transmit the message in the clear. Postfix will
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# accept whatever SSL certificate the remote end provides. Opportunistic TLS
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# protects against passive easvesdropping (but not man-in-the-middle attacks).
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# DANE takes this a step further:
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#
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# Postfix queries DNS for the TLSA record on the destination MX host. If no TLSA records are found,
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# then opportunistic TLS is used. Otherwise the server certificate must match the TLSA records
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# or else the mail bounces. TLSA also requires DNSSEC on the MX host. Postfix doesn't do DNSSEC
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# itself but assumes the system's nameserver does and reports DNSSEC status. Thus this also
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# relies on our local bind9 server being present and `smtp_dns_support_level=dnssec`.
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#
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# The `smtp_tls_CAfile` is superflous, but it eliminates warnings in the logs about untrusted certs,
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# which we don't care about seeing because Postfix is doing opportunistic TLS anyway. Better to encrypt,
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# even if we don't know if it's to the right party, than to not encrypt at all. Instead we'll
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# now see notices about trusted certs. The CA file is provided by the package `ca-certificates`.
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tools/editconf.py /etc/postfix/main.cf \
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smtp_tls_security_level=dane \
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smtp_dns_support_level=dnssec \
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smtp_tls_CAfile=/etc/ssl/certs/ca-certificates.crt \
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smtp_tls_loglevel=2
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# ### Incoming Mail
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# Pass any incoming mail over to a local delivery agent. Spamassassin
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# will act as the LDA agent at first. It is listening on port 10025
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# with LMTP. Spamassassin will pass the mail over to Dovecot after.
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#
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# In a basic setup we would pass mail directly to Dovecot by setting
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# virtual_transport to `lmtp:unix:private/dovecot-lmtp`.
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#
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tools/editconf.py /etc/postfix/main.cf virtual_transport=lmtp:[127.0.0.1]:10025
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# Who can send mail to us? Some basic filters.
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#
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# * `reject_non_fqdn_sender`: Reject not-nice-looking return paths.
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# * `reject_unknown_sender_domain`: Reject return paths with invalid domains.
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# * `reject_rhsbl_sender`: Reject return paths that use blacklisted domains.
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# * `permit_sasl_authenticated`: Authenticated users (i.e. on port 587) can skip further checks.
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# * `permit_mynetworks`: Mail that originates locally can skip further checks.
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# * `reject_rbl_client`: Reject connections from IP addresses blacklisted in zen.spamhaus.org
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# * `reject_unlisted_recipient`: Although Postfix will reject mail to unknown recipients, it's nicer to reject such mail ahead of greylisting rather than after.
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# * `check_policy_service`: Apply greylisting using postgrey.
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#
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# Notes: #NODOC
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# permit_dnswl_client can pass through mail from whitelisted IP addresses, which would be good to put before greylisting #NODOC
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# so these IPs get mail delivered quickly. But when an IP is not listed in the permit_dnswl_client list (i.e. it is not #NODOC
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# whitelisted) then postfix does a DEFER_IF_REJECT, which results in all "unknown user" sorts of messages turning into #NODOC
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# "450 4.7.1 Client host rejected: Service unavailable". This is a retry code, so the mail doesn't properly bounce. #NODOC
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tools/editconf.py /etc/postfix/main.cf \
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smtpd_sender_restrictions="reject_non_fqdn_sender,reject_unknown_sender_domain,reject_rhsbl_sender dbl.spamhaus.org" \
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smtpd_recipient_restrictions=permit_sasl_authenticated,permit_mynetworks,"reject_rbl_client zen.spamhaus.org",reject_unlisted_recipient,"check_policy_service inet:127.0.0.1:10023"
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# Increase the message size limit from 10MB to 128MB.
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tools/editconf.py /etc/postfix/main.cf \
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message_size_limit=134217728
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# Allow the two SMTP ports in the firewall.
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ufw_allow smtp
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ufw_allow submission
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# Restart services
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restart_service postfix
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