[berlam]

This feature is called sub-addressing, but it is also known as plus addressing or tagged addressing.

I also use it but some services do not allow the plus sign in their registration form. Very frustrating.

[brohee]

Rejecting addresses with a plus is to me a strong incompetence clue, so unless somehow unavoidable between two choices I chose the one allowing a '+'.

Sometime I even fire a mail explaining people rejecting '+' how and why they lost my business...

[dbg31415]

I feel the same way. (=