If an end user replies to a schooldude message or has an out of office reply set, messages are not accepted by the SchoolDude mail server smtp.schooldude.com. Outgoing mail servers re-try to send and users get undeliverable messages because they are trying to send to an address that is not meant to receive email. I suggest to you that a Do Not Reply address would be better implemented as a “black hole” that just discards messages instead of an address that causes mail systems to retry until they time out and give up. Most of the messages to smtp.schooldude.com stuck in our mail queue are users out of office reply’s, so they are not intentionally sending them, yet they get queued and eventually bounce back to the user. A black hole would be a cleaner solution. SchoolDude, please consider fixing this.