Update entrypoint.sh: handling `listname[-+](request|owner|bounce|sendkey)@example.com` addresses properly

This fixes Schleuder not handling `listname-(request|owner|bounce|sendkey)@example.com` requests at all; but also enables making those requests even if we're using a GMail (or other large provider) e-mail address, via `listname+(request|owner|bounce|sendkey)@example.com`.