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