And now it works... No changes made to local email configuration or SmarterMail.
I did see this issue slowly start with outage notifications in the local email client and then today the outage was much longer (multiple hours).

So if it self healed, I am not sure what could have been the issue?

The pings to the target port showed success while the outage was still happening.

We did check on multiple devices (two phones and one desktop computer) which would point to it not being a specific device issue.

Maybe local internet provider causing issues? But the successful ping should not have happened if local provider was blocking a port.

I've not erased this thread in case anyone also has a similar issue.

Sounds like IDS.  Maybe an IDS Block for your Mac clients:

Maybe someone changed their password and didn't update their client which generated repeated logins and blocked your IP.

Kevin

I agree the IDS block is the most likely culprit, but without knowing more about the setup those clients are using its tough to say. Are all affected users connecting via secure IMAP on port 993? If so, what hostname do they have configured and were they having any trouble reaching the hostname directly in a web browser or via telnet connection? If you can get a ticket submitted on this one I'd be happy to help dig in.

We are experiencing similar issues for all domains that we host.

Yesterday at around 16:00 (PST), sending emails from server to recipients on other email servers stopped working. We could still send emails from smartermail to smartermail.

No blacklists or blocked IP listed.

This morning, we could send emails from webmail but not from email clients (MacMail or Outlook). Getting Port 465 error.

Still working on the issue right now.

Please let us know if / how the issue was resolved for you. Thanks.

We restarted all of the services again just now, and everything magically started to work.