Report the PM. That is obviously against the rule, he'll be warned or banned if he already did it multiple times.
Edit: @mods Uhh, look at his post history. 100+ posts under 4 hours.
Now he's getting banned for sure.
Yes by reporting to mod is the best way to warn him or banned.
100+ post in less then 4 hours? Its crazy. I think the post is more spam.