[renep]

Originally Posted by Milad

If you have a better pattern to suggest, go on.

I couldn't find an authoritative specification, but it seems '+' is universally used as the box+recipient separator, and '=' is used to encode special characters in the recipient address (that may not be unencoded in the bounce address).

By following this pattern, people can use the default VERP-support in their MTA to route bounces to a particular mailbox, which your add-on reads.

You prefer to use an id rather than the recipient address in the bounce address, to avoid abuse. That's fine of course, as long as you encode special characters in the id (in particular '@').