Open Microsoft Outlook Express and select Tools => Accounts... from the menu. You wil be presented with this screen:

Select the mail account you wish to change and click the Properties button, you will then see this:

Click the Advanced Tab to see this:

The port number you are concerned with is the Outgoing Server (SMTP): If this is currently set to port 25, you do not need to make any changes, you can if you wish, as it can help when you are travelling. If you are currently using port 366, please change this number to 587.

Click Ok until you are back to you mailbox. Congratulations Your Done!