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.
