yes i belive retrieval is where it connects and downloads the entirety of the new email, and notifications is where it only notifies you of the new emails.
the are mutually exclusive because retrieval both notifies and retreives, and notification only notifies.
I have been using niether, and instead just log into my imap mailbox from the phone and keep it connected, that way by default it checks every 5 minutes and notifies me (but does not retreieve unless i specifically ask it too)
However i think that my method is bad because it keeps the wifi always on, and uses a lot of power.
what I am saying is based on the e51, i have not tried it on my
N95 but i assume everything is the same except of the notification LED that the e51 has