Lion Mail 5.0 can't send e-mails through Gmail SMTP

I just had the following problem: Whenever I would send a mail in Mail 5.0 it would go straight to outbox and stay there forever without being sent.

Every once in a while a message popped up asking me to reauthenticate with my password, but doing so did no good. The connection monitor (found in the menu "Window") showed mail trying to connect to the gmail smtp server for long periods of time, but without success.

I finally resolved it by forcing the port for the SMTP server connection to be 587 as is suggested here.