Colin,

if you use private registration mode, the user gets the frist message immediately after registration to verify his address (no delivery failure) and tell him to wait, and the second, when he gets acknowledged by the administrator.

again: if you use  "private" registration, the first email is ssent, when the user itself registers and the second, when a portal admin acknowledges the user.

You can modify the texts by entering the languages item in admin menu (per portal) or host menu (for all portals of the installation). Select language editor, desired language (in host mode use "host" type) and you get immediately presented aoo_globalresources, where you find the keys EMail_...