Hacker News new | ask | show | jobs
by stonogo 1568 days ago
It's not in the SMTP spec because SMTP doesn't need to know about it. Your objection is correct but in fact that's the desireable behavior -- senders can't assume that foo+bar and foo+qux are the same person. If they could make that assumption, subaddressing would be defeated as a useful filter signal. As it is, it's not just plus signs -- qmail has been using '-' as the subadress separator for decades.

Subaddressing is standardized in RFC 5233 as a filtering signal.