I am setting up an email server with Postfix and Dovecot. Remote email clients can read email, but cannot reply to it or send new messages. (Email clients local to the server receive and send email just fine.) For example, Alpine tries until told to give up, when it says "Error sending: SMTP greeting failure 421 SMTP connection went away".
When I run alpine -d 4, the debug output shows:
=== sending: Sending mail... call_mailer: via TCP IMAP 11:34:01 9/14 mm_log babble: Try IP address [xx.xx.xxx.xxx] IMAP DEBUG 11:34:02 9/14: * OK Dovecot ready tcptimeout: waited 15 seconds tcptimeout: waited 30 seconds . . . .
To me, that suggests a problem on the server b/w Dovecot and Postfix. But I can't figure out how to diagnose it.
The server's syslog shows a successful imap-login, but none of the logs (remote or client) seem to have any information about the failure to send the message.
Odds are very good that I've screwed up something in the Postfix or Dovecot configuration (SSL / TLS? SASL?) I'd like to trouble-shoot this without guessing endlessly. So, please:
What is a good process to debug this?
How can I test the interactions among the various processes so I can find the one that is failing?
Is there a way to increase the debugging / logging output of Postfix and Dovecot?
Is there a way to emulate the Dovecot / Postix interaction, and / or the remote client / IMAP server connection, so I can see if these are proceeding as required?