[The Wolf]

I have several different SMTP servers programmed into Mail.app becuase I send/receive email from many locations. In reality, I primarily use only 2 (work and home). Why can't Mail.app figure out which one to use so I don't have to manually set it each time? Is there a way around this?

[cybergoober]

Mail uses the SMTP server of the current account that is selected (i.e. Let's say you have three accounts - Home, Work and Play and each has its own SMTP server setup. If you have a message selected in your In box that is associated with your "Home" account, when you go to compose a new message it will use that SMTP server).

[Diggory Laycock]

It's very irritating - the best option is to just use one SMTP server per account that will work anywhere - the best way to do this is to use the right port for authenticated SMTP (and use authenticated SMTP.)

Some ISPs block port 25 - which is the port for unauthenticated mail transfer.