As ISP’s and webhosts are starting to offer alternative ports for SMTP, some may ask how to change the port in Mozilla/Thunderbird. So here is a rundown step by step (don’t worry, it’s really easy).
Go to Mail, then in the Edit menu select “Mail & Newsgroups Account Settings”
Go into the Tools menu and select “Options”
Go down to “Outgoing Server (SMTP), and change the “Port” to the desired port number
That’s all there is to it, you will now connect with the desired port.
Contact your ISP for a list of alternative ports.