But I need help fixing this specific problem, so I thought I'd open a new thread to ask for troubleshooting.
I have one email account on this server - I regularly receive mail, but today was the first time since the fateful update that I tried to send a message. At first the complaint in Thunderbird was a mysterious "The mail server sent an incorrect greeting," but after turning off Avast's outbound mail shield, the complaint changed to a simple timeout, so I started looking at the server end.
I wish I had a snapshot of my Postfix settings from before the update, but I don't. As far as I know my settings were pretty ordinary. I had been using port 587 with STARTTLS, and I had not touched any settings in Thunderbird. But checking netstat, one problem was obvious - no listening ear on the port at all!
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$ netstat -tlpn
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 127.0.0.1:3306 0.0.0.0:* LISTEN 26663/mysqld
tcp 0 0 0.0.0.0:110 0.0.0.0:* LISTEN 1346/dovecot
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 2294/nginx: worker
tcp 0 0 0.0.0.0:1010 0.0.0.0:* LISTEN 7525/perl
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 25060/sshd
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN 1860/master
tcp 0 0 0.0.0.0:995 0.0.0.0:* LISTEN 1346/dovecot
tcp 0 0 127.0.0.1:9000 0.0.0.0:* LISTEN 27655/php-fpm: mast
tcp6 0 0 :::110 :::* LISTEN 1346/dovecot
tcp6 0 0 :::1010 :::* LISTEN 7525/perl
tcp6 0 0 :::22 :::* LISTEN 25060/sshd
tcp6 0 0 :::25 :::* LISTEN 1860/master
tcp6 0 0 :::995 :::* LISTEN 1346/dovecot
tcp6 0 0 ::1:9000 :::* LISTEN 31173/sshd: root@pt
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tcp 0 0 0.0.0.0:587 0.0.0.0:* LISTEN 1860/master
tcp6 0 0 :::587 :::* LISTEN 1860/master
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$ telnet localhost 587
Trying ::1...
Connected to localhost.
Escape character is '^]'.
220 mail.mydomain.com ESMTP Postfix
ehlo test
250-mail.mydomain.com
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
quit
Connection closed by foreign host.
But now what should I test or look for? Just like I described in my other thread, this yum update seems to have messed with stuff it shouldn't have messed with, and I have no idea how far the damage goes. In this case, I assumed that Postfix must have been one of the 200+ packages that were updated that day, but it's currently on version 2.10.1, which is three years old (I guess that's the newest that CentOS7 will bundle), so probably not. "yum history" is no help - it says this:
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$ yum history list postfix
Loaded plugins: priorities
ID | Login user | Date and time | Action(s) | Altered
-------------------------------------------------------------------------------
1 | System <unset> | 2017-02-03 04:49 | Install | 297
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