Too many user emails domains not working lead to mailgun domain disabled: what to do?

But if there are a zillion email addresses like bademail.domain, maybe what you want to do is something like

rake posts:remap['bademail.domain', 'no-email.invalid']

as described in Replace a string in all posts. That will make all of those email addresses such that Discourse won’t send to them. Another good solution would be something like

bad=User.find_by_email     <some search that will get them all>
bad.update_all(active: false)

and deactivate all of the users with the known bogus email addresses. Not quite sure how to do the first bit off the top of my head, but it should be easy enough to figure out.