Email will not "synchronize" to the BlackBerry. they are forwarded at the time they arrive by either a BIS account, a BES, or the desktop redirector. ie. say you bought your 7290 3 days ago, and got it set up in 10 minutes. You will have email on the handheld from 3 days ago (after setting it up) till now, but you will NEVER have emails older than what the date was 3 days ago.
If you are not on a BES (corporate BlackBerry server) then you didn't need to do an Enterprise Activation.