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I get this warning from postfix-2.7.1

Apr 18 13:08:40 bar-work postfix/smtp[5112]: warning: mx-foo[10.132.10.100]:587 offered no supported AUTH mechanisms: 'GSSAPI NTLM'
Apr 18 13:08:41 bar-work postfix/smtp[5112]: certificate verification failed for mx-foo[10.132.10.100]:587: untrusted issuer /CN=FOOEXCH01
Apr 18 13:08:41 bar-work postfix/smtp[5112]: C9D0F10D5770D: to=<user@example.com>, relay=mx-foo[10.132.10.100]:587, delay=0.55, delays=0.01/0/0.37/0.18, dsn=2.6.0, status=sent (250 2.6.0 <20120418110840.22315.51521@bar-work.example2.intern> Queued mail for delivery)
Apr 18 13:08:41 bar-work postfix/qmgr[2926]: C9D0F10D5770D: removed

First postfix says it can't find a supported auth, but the mail gets delivered. Which auth method succeeded?

I ask out of curiosity, because the service works like it should.

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1 Answer 1

up vote 1 down vote accepted

Apr 18 13:08:40 bar-work postfix/smtp[5112]: warning: mx-foo[10.132.10.100]:587 offered no supported AUTH mechanisms: 'GSSAPI NTLM'

  • postfix connects to mx-foo.
  • mx-foo responds with 220 and, among other capabilities, AUTH
  • postfix tries to negotiate an authentication mechanism
  • the server only advertises GSSAPI and NTLM, which postfix does not support

Apr 18 13:08:41 bar-work postfix/smtp[5112]: certificate verification failed for mx-foo[10.132.10.100]:587: untrusted issuer /CN=FOOEXCH01

  • postfix now tries STARTTLS, since the remote server may be configured to only offer AUTH after TLS is established
  • postfix fails to verify the server TLS certificate, but continues with a warning
  • mx-foo does not offer AUTH after TLS

Apr 18 13:08:41 bar-work postfix/smtp[5112]: C9D0F10D5770D: to=, relay=mx-foo[10.132.10.100]:587, delay=0.55, delays=0.01/0/0.37/0.18, dsn=2.6.0, status=sent (250 2.6.0 <20120418110840.22315.51521@bar-work.example2.intern> Queued mail for delivery)

  • postfix submits a normal message
  • the message is accepted

I suggest you don't attempt AUTH in the first place, by fixing this in main.cf:

smtp_sasl_auth_enable = no

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thank you very much for this detailed explanation! –  guettli Apr 18 '12 at 12:08

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