How to authenticate Mac Mail when connecting through another ISP (Comcast is used as an example, your ISP will provide you with their settings)

Launch MAIL by selecting it from the dock.

Open Mail options from the top menu and select Preferences

Select your email account in the Accounts screen an then click on the Edit button.

click on Account Information

In the SMTP Server Options, change the Server port to 587. Make Sure that Authenticate is set to Password and enter your e-mail user name and password in the designated fields