Associate The Bat! with specific file types/URLs – check which files you want to associate with The Bat!. You also associate mailto: URLs here.
Simple MAPI - Simple MAPI is an interface for other programs to work with e-mails. Install The Bat! as Simple MAPI handler if you want to send e-mails directly from your dtabase or word processing application.
Check that The Bat! is the default mail client at startup – since some programs install themselves as the system's default e-mail client you can automatically let The Bat! check that it is the system's default.