Hey its private property, there using your resources and your vBulletin you can do what you like.
I don't see hotmail with it in there privacy statement, but if someone abuses the hotmail account you forward the message to
abuse@hotmail.com and they check the account to see if they have been abusing it... Whats the difference with this hack?
people send you emails about abuse, you check the pm account and if you find abusive emails, you deal with it.
Scott