I agree with Kogas on this one. If someone is sending you harassing PMs, you can just delete them unread.

Banning because of PM presents a slippery slope. What if they are sending messages to your email?

Hopefully, when the software is updated, it will include an "ignore this user" function.
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In my walk in the martial way, my hope is that as long as I live, I will always be a beginner.