Re: Why do so few mail providers support Port 587?

[Sean Donelan <sean () donelan com>]

Yet another reason for supporting port 587 on your servers for remote
authenticated mail submission from your users.  If you don't support
port 587, and use SPF, it may break when AOL or other providers re-direct
port 25.

http://www.heise.de/english/newsticker/news/56437

> with many questions related to this topic." The company was advising AOL
> customers affected to switch to message submission port 587, the signals
> from which were not being filtered by AOL, the spokesman said. This item
> of advice on switching coincides with that given by AOL itself. Not all
> mail providers accept messages from this port, however; and not every
> mail client allows users to freely select their SMTP port.