gmail

gmail allows between the localpart and @gmail.com the following 19 special ascii characters

^ $ % & / ( ) ` * ' = ? + # { } ~ ! |

Important is the + after the localpart.

Spambots can't handle this kind of e-mail addresses
You can't use:  , ; : < > [ ] and more @'s
 
 
gmail fails to forward the above address via a forward to filter, but "forward all" works