On a regular basis, I get emails from vaguely reputable entities (airlines?!) sent with the wrong date. For example, on Wednesday I'll get a message "sent" on Monday. Because these messages show up out of order in a mail reader, and are marked "unread" among mostly "read" messages, they catch my attention. And sometimes I read them.
It's time to call this out for what it is: an annoying spamming technique designed to try and get my attention. And, like sending all your email flagged "High Importance," it gets old fast and makes you look bad.
There are plenty of time servers on the net. Plenty of bulk mailing mechanisms that don't get several days behind in getting the mail out. And plenty of docs on how to leverage UTC and offsets in your environment of choice.
So I don't believe anymore that a "misconfigured server" or "backed up bulk remailer" is to blame.
If I were an ISP, I'd think about creating spam filter rules that tweak an entity's rating every time bulk mail comes through with a date that's way off. Do this enough, and your messages go to my users' filtered spam folder.