Date: Tuesday, June 16, 2015 07:05:43 PM -0400 From: Steve Matzura <number6@noisynotes.com>

On Tue, 16 Jun 2015 17:31:07 +0000, you wrote:

...

By default, most MTAs only listen to localhost, so don't accept externally derived mail. Try telnetting to port 25 on the machine from some place off your machine's network. If you get a "hang", it's likely a firewall issue. If you get a "connection refused" message it's probably that the MTA isn't listening on the external interface.

If the MTA responds, do a manual delivery exchange and see what you get.

If you're not seeing anything in your maillog, this is very likely an issue with your MTA's configuration, not dovecot.

Now that I think about and concentrate on what you wrote, make perfect sense. Add to that the fact that I received bounces from my ISP that all said the same thing: Unable to establish an SMTP connection. The return code was 4.5.1.

A 4xx indicates a transient error (i.e., within configured limits, delivery retries will be attempted), 5xx is permanent (immediate reject, no retries), otherwise the specific number isn't all that telling.

From everything you've indicated, this is an MTA issue.