When an alias has a remote destination, chasquid uses sender rewriting
(also known as SRS [1]) to forward the email without risking being in
violation of SPF policies.
See https://en.wikipedia.org/wiki/Sender_Rewriting_Scheme for more
details.
This, however, wasn't documented anywhere, as noted in
https://github.com/albertito/chasquid/issues/6.
This patch adds a paragraph to the alias documentation explaining this
behaviour.
This patch implements two new hooks: alias-resolve and alias-exists.
They are called during the aliases resolution process, to allow for more
complex integration with other systems, such as storing the aliases in a
database.
See the included documentation for more details.
