[dane] Postfix 2.11.0-RC2 available with feature-complete DANE support

Viktor Dukhovni <viktor1dane@dukhovni.org> Fri, 10 January 2014 00:17 UTC

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Date: Fri, 10 Jan 2014 00:17:26 +0000
From: Viktor Dukhovni <viktor1dane@dukhovni.org>
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Subject: [dane] Postfix 2.11.0-RC2 available with feature-complete DANE support
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Postfix 2.11.0 is now in code-freeze.  With 2.11.0-RC2 the DANE
support is feature complete, and matches the DANE SMTP draft.

The official 2.11.0 release will happen in the next couple of weeks.
Test feedback welcome.


While I am busy with IETF drafts, some brave souls have volunteered
to contribute a more consolidated DANE_README tutorial.  I'll post
a link here when/if all goes well on that front.  Currently the
DANE related information is scattered over a few documents.

Minimal client configuration:

    Note: A DNSSEC validating resolver MUST be present on the
    LOOPBACK interface and MUST be the only resolver listed in
    /etc/resolv.conf.  Postfix delegates DNSSEC processing to the
    system's caching resolver.  A local resolver is in any case a
    good idea for an MTA that handles non-trivial mail volumes.


	smtp_host_lookup = dns
	smtp_dns_support_level = dnssec
	smtp_tls_security_level = dane
	ignore_mx_lookup_error = no

Recommended Server DNS configuration:

	example.com. IN MX 0 mx.example.com.

    Publish one of the two TLSA record forms below, the remaining
    22 combinations have little to recommend them:

	; Per-service EE SPKI TLSA RR:
	_25._tcp.mx.example.com. IN TLSA 3 1 1 {EE SPKI SHA2-256 digest}


	; Domain-wide TA CERT TLSA RR, aliased from each service:
	_25._tcp.mx.example.com. IN CNAME 2.1.1._tlsa.example.com.
	2.1.1._tlsa.example.com. IN TLSA 2 0 1 {TA CERT SHA2-256 digest}

    In the second case the domain-issued TA certificate MUST be
    included in the server chain file:

	# cd /etc/postfix
	# cat ee-cert.pem intermediate.pem ... root-ta.pem > chain.pem
	# postconf -e 'smtpd_tls_security_level = may'
	# postconf -e 'smtpd_tls_cert_file = ${config_directory}/chain.pem'
	# postconf -e 'smtpd_tls_key_file = ${config_directory}/ee-key.pem'

    and the ee-cert MUST have at least one of "mx.example.com" or
    "example.com" as a DNS subjectAltName or subject commonName.

    Avoid wildcard certs, they may allow MITM attackers to redirect
    connections to the wrong hosts.

See http://www.postfix.org/FORWARD_SECRECY_README.html for additional
server TLS tuning.