Sometime over the past few days my Postfix config seems to have gone awry. It has not been delivering SMTP messages to external servers for several days. After restarting Postfix and rebooting the machine did not help, I dug into the logs and what I am seeing is pretty much this:
status=deferred (delivery temporarily suspended: connect to alt2.gmail.smtp-in.l.google.com[2607:f8b0:4002:c01::1b]:25: Connection timed out)
Gmail is not the only domain showing this issue. It ranges from other big domains like Yahoo to what appear to be small individual sites.
I did not have reverse DNS/PTR entries set up, so I remedied that but it has not helped the issue. I checked my IP against spam blacklists and it is clean. I have manually telneted to port 25 for the Google server above and can connect with no trouble, it responds to a HELO command, etc., so there does not appear to be a network connectivity issue.
I'm at a loss as to what to check next. I'd appreciate any guidance you folks might have.
On another note, since adding reverse DNS entries my email clients can no longer send email using their domain's SMTP server (with authentication). I am now getting "Relay access denied" errors. I see I can enable relaying in the Postfix settings, but I'd like to know how to do this in the most secure fashion, and I'm wondering why this issue just popped up now -- I've been sending emails to external domains using secure SMTP for awhile now.
EDIT: Disabling CSF firewall fixed the outbound mail problem, puzzling since ports 25/26 were open for in and outbound traffic. We'll see if it behaves once CSF is restarted.
On the SMTP authentication note, I believe the problem is with saslauthd not running. I've tried restarting it, but it appears it is not configured properly anymore -- it won't run and asks that I select an authentication method. How can I configure/reinstall this package so it plays nicely with Virtualmin?