Just look around the repository, I think your situation might similar to issue 3757
https://github.com/LemmyNet/lemmy/issues/3757
Quote:
[...]You're saying when someone requests their password 3 times it completely breaks email for the whole instance for 24 hours?
No just for that user for 24 hours
Wait 24 hours, then try to register again with different email. If no avail, you might need to ask the admin for help on the verification email issue.