How do I transfer my old mail to my new Lion mail.app
In the IMAP protocol, all E-Mails are stored and managed on the server. This allows multiple clients on different computers to manage the same mailbox.

By default, the Mail.app in OSX Lion also stores Drafts, Notes and Sent Messages on the server.

Just setup your mail account in System Preferences &#x2192; Mail, Contacts &amp; Calendars and you should be fine. Your E-Mails will be downloaded from the server.