Mail.App under Macos X

Open Mail.app
In the Mail menu, select Preferences
Click the Accounts tab
Select the account on the left you wish to edit
On the Account Information tab, find “Outgoing Mail Server (SMTP):”
Click the arrows for the dropdown menu, and select Edit Server List…
Make sure the server you wish to use is selected in the list, and click on the Advanced tab
In the Authentication dropdown, select “MD5 Challenge-Response”
Type in your SDF username in User Name field
Type in your password in Password field
Click ok, and close the Preferences window.

SDF User Contributed Tutorials