I've spent a couple of hours this morning sorting out some email problems for clients. Three clients have reported problems sending emails out over the last couple of days.

Two were using Outlook on Windows based PCs and one was using Entourage on a Mac.

To further complicate things, one client was in Spain.

So it was difficult to immediately identify any commonalities. This made sorting out the problems a little more tricky.

To cut a long (2 hour) story short, it would appear that the standard port used to communicate with an SMTP server (usually port 25) seems to be having an off day!

iMail on the Apple Mac has a list of three Ports is us
es. I guess this means that if one port isn't listening then it tries the next in the list??
But the poor clients using Outlook on Windows computers don't appear to have the luxury of trying multiple ports. So when port 25 seemed to have given up the ghost when these clients were trying to send emails, the sending process just failed.

The clients were trying to send out emails, but Outlook was reporting that the SMTP server was not responding (this wasn't exactly true as I managed to PING the servers and get a response).

To resolve the problem I have manually overridden the default port 25 and used port 587 instead.

Why on earth I've had to do this I don't know.

Anyone else have any bright ideas?