I've read that spammers who used to join forums to post their spam (and be quickly banned) have yet another tactic: joining forums and sending junk PMs to as many people as possible. We haven't had many reports about this, at least so far, but we know it's a possibility. A minimum time between sending private messages prevents instant mass mailing of PMs, but it will certainly be an annoyance for all of us if unwanted junk PMs become a regular problem. Adding a minimum post count required for PMing could help a bit.
If you encounter this problem, or get any other type of unwanted PM, let us know. Tell us who sent you what by PM so we can take the appropriate action.
Rather that pick a particular moderator, it's best to use the Report Post system (that icon next to each post) to send us a message. It goes to the moderator "on duty" and works better than trying to tell or guess who's online at a given moment. You can't always tell.