By default, you can't receive PMs from Newbie accounts. You need to opt-in for that.
In response to the annoying PM spam, you now have to opt into receiving PMs from newbies. The option is in your
PM preferences. You also can't
send PMs to newbies if you haven't opted in. Copper members are exempt, but only if you're wearing the copper membership.
You should opt into receiving newbie PMs if you post offers in the marketplace, if you like answering newbie questions, if you're a moderator, etc.
To start with, if you sent a PM
to a newbie in the last 30 days, you're already "opted in".
I don't think I have ever received spam PMs on this forum, to be honest.