Apparently, and much to my surprise, there is more than one mbox format.
I just now stumbled across this, because I am going to be (re-)writing
some small tools I have that do useful things with mail messages stored
in "mbox format":
https://en.wikipedia.org/wiki/Mbox
In the above Wikipedia page, four different flavors of "mbox format"
are described: mboxo, mboxrd, mboxcl, and mboxcl2.
When Postfix hands a message to something... say a script invoked via
some ~/.forward file... which one of these four formats will the message
be in?
