Microsoft Entourage

Open Entourage.
Select Tools > Accounts from the menu at the top of the screen.
The Accounts window should appear. Click on your email address and click Edit on the toolbar above the tabs.
The Edit Account window should appear. At the bottom of this window is an area titled Sending Mail. Click on the button labeled Click here for advanced sending options.
Make sure the checkbox next to the words SMTP server requires authentication is checked.
Check the box for "Save password in my Mac OS keychain"
Make sure the circle next to Use same settings as receiving mail server is selected and click OK.
You'll be returned to the Edit Account window. Click OK.
You'll be returned to the Accounts window. Close the window.