Delete an Email Address from Auto-Complete in Mac OS X Mail

To remove an email address from the auto-complete list in Mac Mail (New verson on Mac OSX):

• Start typing the recipient's address or name in a new message.
• Select the desired address from the auto-complete list as if you'd compose an email to them.
• Click the small down arrow in the recipient or complete then Right Mouse Click.
• Select Remove from Previous Recipients List from the menu.

You can also search for the unwanted address directly in the previous recipients list:

• Select Window | Previous Recipients from the menu in Mac OS X Mail.
• Highlight the address you want to remove.
  • You can highlight multiple addresses by holding down the Command key.
• Click Remove from List.