[UPDATE: The issue fixed itself. I am thinking the relay server which in this case Sendgrid had something to do with this.]

Everything was running smoothly until the Dovecot version got updated to 2.3.8 on my CentOS 8 server or at least that's when I start noticing it. Inbound mails are fine and transactional mails from my WordPress site are also sending. I am using Postfix, Dovecot and virtual mailboxes via PostfixAdmin. These are the content of the maillog:

Jun 30 13:34:10 bluesky postfix/smtp[950050]: error: open /etc/postfix/smtp_header_checkssmtp_address_preference: No such file or directory
Jun 30 13:34:10 bluesky postfix/smtp[950050]: fatal: open dictionary: expecting "type:name" form instead of "="
Jun 30 13:34:11 bluesky postfix/master[811267]: warning: process /usr/libexec/postfix/smtp pid 950050 exit status 1
Jun 30 13:34:11 bluesky postfix/master[811267]: warning: /usr/libexec/postfix/smtp: bad command startup -- throttling

The only change I did since the Dovecot update was the ssl_dh parameter since it complained about the length and about not supporting SSL - if this has something to do with the issue...

  • These aren't errors from Dovecot. Have you read the messages and addressed the two errors it's reporting to you? – roaima Jun 30 '20 at 6:57
error: open /etc/postfix/smtp_header_checkssmtp_address_preference: No such file or directory

This error is from Postfix, and it looks like two lines have been accidentally merged together in a Postfix configuration file. /etc/postfix/smtp_header_checks looks like a value for the smtp_header_checks setting, and smtp_address_preference is supposed to be a separate configuration item. It might be just as simple as a single missing newline character here.

fatal: open dictionary: expecting "type:name" form instead of "="

This is again from Postfix, and might be a consequence of the previous error. Or it might be a separate problem.

The two other messages are definitely resulting from the previous errors. Because of the previous configuration error(s), the smtp process of Postfix failed to start, and now the master process reports that fact too.

Since the problem only occurs with sending outgoing mail outside this system, a problem with Postfix's smtp process definitely could be the root cause. Dovecot, on the other hand, deals mostly with mail clients and their access to the local mailboxes; it has very little to do with outbound mail.

  • You are correct. The last two lines in main.cf got merged for some reason and now the error is gone. But I'm still not getting the emails even though I see dsn=sent in the log. – Joey Jun 30 '20 at 8:38
  • dsn=sent where? Was that just Postfix's answer to the local mail client as it took in the mail, or the response from an external destination mail server as it took over responsibility of delivering the mail to the recipient? Are you sending all outgoing email through a specific server ("smarthost configuration") or is your mail server sending directly to the recipient's mail server? – telcoM Jun 30 '20 at 8:53
  • I'm curious in the 'queued' part... "Jul 1 01:38:40 bluesky postfix/smtp[1037611]: F317A1C86893: to=<recipient@outlook.com>, relay=smtp.sendgrid.net[]:587, delay=2.1, delays=0.68/0.05/1.3/0.07, dsn=2.0.0, status=sent (250 Ok: queued as uYQQpo_ZSg-tutL84_bfog)" – Joey Jun 30 '20 at 22:37
  • The alphabet soup after "queued as" is apparently the queue ID of the mail in the smtp.sendgrid.net server, similar to F317A1C86893 that was used in yours. Different mail server software use different queue ID formats. You could now contact the smtp.sendgrid.net administrator and ask: "I sent an email through your server at Jul 1 01:38:40 and your server received it with queue ID uYQQpo_ZSg-tutL84_bfog. Can you please find out what your server did to it, and if it was discarded as spam, please tell me what kind of test it failed?" There's not much else you can do with a queue ID. – telcoM Jul 1 '20 at 4:47

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