I've just changed my ISP from AT&T's DSL to AT&T Uverse, and found that port 25 is now irrevocably blocked for my new account; it had been grandfathered on the DSL account. As a result, my local mail server is no longer able to send traffic outside my LAN. While I don't need to do so often, since I keep an off-site non-ISP server for normal use and it allows alternate ports, I have a couple of programs that do need to send things, and I sometimes reply to messages that come into my local server.
EDIT: Cut to the chase; solution is in message #10.
The simplest solution to this problem would be to change settings of postfix to use port 587 instead of 25. However I've not been able to find anything in the documentation or the configuration files that gives me any hint of how to accomplish this change. None of the how-to pages I've read mention the subject, and a forum search turned up exactly one post that mentioned making such a change -- and it failed to say how or where it was done. Can someone please enlighten me?
If no such setting exists, is there a way to use iptables, specifically the OUTPUT chain of the nat table, to handle things?
Many thanks for all responses!