How do i correct an incorrect email address?
First check if the incorrect address is in Contacts. If so, you can just edit and correct it there.

If not, then it is probably stored in the address history. You can open this from the Window->Previous Recipients menu. You can search for the address in the dialog and delete it. (You might need to do this, even if you edit the email address in Contacts, as the wrong address might have been stored in the history.)