he sends me abusive private messages in which he says that he will be as much of the word I am not allowed to call him as he likes, and if I don't like it, tough. Then he deletes the PM; given that he has always used the original one from our first off-forum chat some years ago, it removes quite a lot. This is a pretty flagrant abuse of mod power.
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I also said somewhere, but can't be bothered to dig up, that if it is the policy to allow this, then something should be done about receiving email alerts to PMs, because the text of a PM shows up in the email. If the intention of deleting the PM was to prevent me from revealing what was said at any point in it, it wasn't thought through. However, I have already given my assurance to my correspondent that I would not reveal anything that was said previously, when we were on good terms.