I am seeing
messages in my rejected email log from email replies to messages.
It does not appear that the user is notified that his message has been rejected, as there does not appear to be an email to the user in that time frame.
Some years ago there was a topic in which it was suggested that an email post that is rejected because of ratelimits should be requeued to try again 30 seconds later.
Was this suggestion ever considered for implementation?