If one is running their own mail server they can reject emails from the sending server assuming one is fine with blocking all email that could come from it. Blocking Gmail for example would be a large blast radius for some. Another less useful option would be to write spamassassin rules that detect AI generated text and subtle signals that AI leaves behind.

If using a third party hosted email solution then I suppose all one could do is to report all the emails to them as spam and see if they have an advanced tuning option to change the threshold for spam detection after reviewing the spam score headers in the emails. Fastmail has such a thing. One can silently discard anything above a specific spam score threshold at the risk of losing legit emails from friends or associates using spammy servers. The headers of the email could also be submitted to SpamCop [1] after configuring a few things in ones account.

[1] - https://www.spamcop.net/