Tom, I have to strongly disagree.
As I've pointed out, bullies flourish when they can act unseen. This is personality disordered behavior (if I may put on my professional hat for a moment). It's due to lack of appropriate internal controls to structure behavior. The solution that works is not to yield ground but to provide external structure. Put plainly, that is about push back. One doesn't need to get riled. _One just needs to get clear, then act._ His behavior is unacceptable. Period. (And that's putting it politely.)
The next person he does this to may be a 12 year old struggling to get a grip on the software and making a mess of it. You want to turn him loose to have at her? Really? I don't think you, and others, have really thought this through.
He knows he's being watched, and yet he acts as if there is no problem for him at all. Why? _Because there isn't_. That needs to change.
I suggest two solutions: he should be banished from the list. If he comes back, repeat as needed.
And, until action is taken, all inappropriate emails from him or anyone else should be forwarded to the list. "No cover for bullies," as I've already said.
I've dealt with people like this on other lists, in my neighborhood, at work (my boss!), and in adolescent treatment centers and mental hospitals. It's always the same drill. One warning, then you lower the boom, decisively. Someone WILL be in control: it's them or it us. We have to decide.
I DO expect an appropriate and effective response from this list, not some ineffectual roll-over.
Tom