There was an issue on phpbb.com and many other forums where spammers were using the private messaging system to send bulk PM's to thousands of members. Actually caused major issue on phpbb.com and yours truly was rousted out of bed to ban the user as there was no other moderators present when it happened. Who's calling ? LOL
In any event there is new option fo limiting the PM's you can send to multiple users however I neglected to set the limits up. You should be able to send up to 3 recipients now.