Hi there! You aren't receiving those out-of-office replies because we actually include a line in the message header that reads something like, "This is a bulk email. No need to reply with autoresponders." Most receiving servers pay attention to that and don't bother delivering out-of-office replies, but some don't.
We actually aren't able to customize this on a per-account basis. Some auto-responders will still sneak by that message, so you may still receive some periodically.
I hope this helps! Please let me know if you still have questions.