Example app illustrating legit use of +all

[sdgathman]

The HELO field is ignored by Big Email, and rDNS demanded instead - mostly because so few admins could manage to actually put the hostname in HELO. I never understood why.

There have been some demands to remove +all - because some admins are using it dishonestly or incorrectly. Having examples of how to use it effectively (and honestly) might help forestall +all meeting the same fate as HELO.