Filter them
I had one customer who filtered out all auto-reply emails at the server level and binned them.
Then they had the nerve to escalate our lack of reactivity to their urgent support emails when the requestees didn't receive any OoO outlining their alternative points of contact for support.
Went all the way up to senior VP shitstorm level.
And even after we sussed what they were up to, the blame was still ours and to my knowledge they still do have this filtering in place.
Biting the hand that feeds IT
