I had one more thought on the idea that rejection, etc., should not be done "automatically" lest nefarious individuals take advantage of the situation:

I submit that having groups.io send a "This topic is locked" rejection notice in response to attempted posts to a locked topic is really "automatic." The rejection notice has, in effect, been requested by the moderator who locked the topic. It is simply a blanket (although still explicit) request at one level "up" from rejecting an individual message. Groups.io would simply be acting as the moderator's agent in sending the boilerplate message.
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J

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