That is exactly the information that we need
Port 25 is not able to be used...and it has probably been disabled by your ISP. mine was disabled by SBC and i had to call them up to reactivate it. Is your e-mail through your service provider or through a third-party? I'm guessing since you are having a problem, you use a third-party to send and receive your mail. I would just call up your ISP and ask them to allow you access to port 25 again.
ok...just looked again and saw you have a .mac account. Try this first. When in mail, from the top bar open mail, preferences, accounts, account information. click on the bottom button which says "server settings" and change the port information from "25" to "587" (thanks FFL). that should work for sending mail...if that doesn't work, you'll have to call your ISP.
hope this helps...