1. Go to Edit | Preferences | Identity 2. In "Email Address", enter [username]@[yourdomain].com 3. In "Reply to...", enter whatever@[yourdomain].com 4. Go to Mail&Group 5. In "Mail server user name", enter [username] 6. Outgoing Mail(SMTP)* server: mail.[yourdomain].com 7. Incoming Mail(POP3 or IMAP)server: mail.[yourdomain].com 8. Click "OK".