Family Tech Support: Managing Previous Recipients in

It happens to all of us. We’re addressing a mail message when some previous recipient, a mis-typed email address, ex significant other, work alias for a good friend, auto-completes in the recipient field. We blithely send the mail message and it doesn’t go where it needs to go.
Apple makes this problem go away with Mail 3.0 in Mac OS X.

“Managing addresses in the Previous Recipients list
When you send messages, Mail stores the recipients’ email addresses in the Previous Recipients list. When you want to send new messages to those email addresses, just type a few letters in an address field and Mail automatically fills in the rest.”
Go to Apple’s support document for the full scoop!
This applies to Mac OS X Mail 3.0 (Mac OS X 10.6 Snow Leopard) and may be different in other versions of Mac OS