"So what do we do about this? Anyone have any ideas?"
Like I said, perhaps we could just disable messages that are known chain-letters (be it by . Yes, the spammers could just add an extra dot or change some words around to avoid it, but at the least they'd have a harder time automating everything. The effort would go from a few minutes of clicking on a bot to a couple hours creating diverse spams and setting up a bot that picks from several messages. The NG admins/Mods/whoever would just have a list where they copy/paste known letters in and can have several different "blocked" paragraphs at a time.
It can also make spam messages more apparent if the writer/coder is lazy and just adds a string of gibberish at the end to make the message different enough to go through.
"Hello. I am from FreeingMusic. We like your stuff, join us. asdlfk!@df I like cats."
In the end, if a user tries to send several people blocked messages enough, they are automatically banned. If the account really is a junk one, the perpetrators probably won't waste time trying to appeal.
Regardless, though, perhaps this would be overly difficult or complicated to code. I am not one to know as such. =P
There's also probably a few options regarding account registration itself, but because I haven't even looked at the registration page since 2009 (and don't know much about coding) I can't delve into that.
Even knowing how they detect who to send the messages to would be helpful; do they just sort people by their aura (musician, artist, etc)? Do they just run down the audio portal and spam artist names? Do they fish around in the forums? All three? Is their sorting method manual or automatic? Perhaps there is a way to block them at that stage.
Furthermore this whole fiasco wouldn't just apply to the music portal either; such a discussion would apply to Newgrounds in general even if the first notice was regarding music spam. Might be worth its own topic somewhere.