Robert Sharp:
> Hi,
>
> I have been trying to use a third-party backup provider to cover
> occasional outages (SiXwishlist). I set up an MX record as instructed
> but I get no emails sent on when my server recovers. I asked them to
> check what was happening and they told me my port was not open. It seems
> they were expecting postfix to be listening to port 4000. I asked for
> clarification and got a response that they would send emails on 587,
> 2525, 3000, and 4000, but that 25 was not recommended and "is blocked
> for 90% of service hosting providers".
>
> I thought that smtp/25 was the backbone of email systems. I use 587
> internally for submission so I don't see why I would make it accessible
> to the outside world. Do I need to open another port? Have I got port 25
> wrong all this time? Or do I need to get myself a proper backup provider?
What you describe sounds more like a primary MX service to me where
the typical customer is behind a port-25-blocking provider.
A downside of not using port 25 for forwarding is that you now also
need to maintain service on a different port, but there is no reason
why it could not be done, if it is based on mutual agreement.
Wietse
