[equoid]

Regrettably a significant number of back ends (principally Microsoft ones in my experience) regard the +bit as malformed and reject the email address.

[SixSigma]

Actually yes, I remember now that's why I use - in my Postfix instead.

Postfix allows you to choose any character as a separator.

[cpach]

Yep. But it can be circumvented if one’s mail server use another delimiter. E.g. ”.” will hardly be filtered.