[noja]

huh? Google's special behaviour is that they are blind to dots in the user part of the address.

The + sign is not anything to do with Google.

[thanksgiving]

Oh I didn't know. Just found https://tools.ietf.org/html/rfc5233 after trading what you wrote.

I just assumed + is a valid character and [e-mail] would be a valid email address independent of a or b. But it seems we shouldn't allow + or -- when people sign up for a new email address?