I've just received a spammy private message.
My email provider did not classified it as spam, even if its content is spam.
The sender is "firstname.lastname@example.org" (this is how private messages work)
I've see that the only option to fight spam on private messages is this one :
Rate limit for private and wall messages
Isn't it possible to have also captcha ?
I saw this question/request had also been posted here
I'd also define a minimum points limit required for a user to be able to send a private message.
Furthermore, since private messages if I'm not wrong are not listed on q2a, it's not possible to flag them (as you can do with the other posts)
If there are no plans to add more "private messages" management features in the next future, I think it should be possible at least to flag users.