A reasonable solution would be if all buff emails in the inbox and/or the outbox could be 'one-click' selected from a context menu for mass deletion. One at a time in the inbox, and not at all in the outbox, is not useful. The outbox especially, with only 50 (or 49) email kept, one set of 50 buffs on a friend's island clears the outbox by filling it with the useless outgoing 'you buffed a friend's building' notifications.