Fastmail supports [email protected] -> [email protected], which is even better

I've even started seeing registration systems that tell me that I've entered an invalid address if I do the [email]+[something]@gmail.com trick.

Twice now I was only able to register after removing the +[something] part of the email.

Is + actually an invalid email character (according to RFCs etc?). I couldn't find any reference to that when I looked.

I'll try to avoid ranting here, but anything is a legal email address per the RFC (even an @ sign in a username, or an email address without any @ sign).

RFC 821 is the original and 2821 summarizes it plus the few that came after to add and clarify.

The only true "RFC email validity check" is to send an email to whatever address they provide.