Calling a user's program to deliver mail

[greep%su-dsn at sri-unix.UUCP]

MH has had this feature (calling a user's program to deliver mail for him)
for quite a while, although it is used mainly to implement the "news"
(bboard) feature.  (In that case the program is a simple shell file.)
One feature I added here is to allow local addresses of the form
"user.mailbox", where what comes before the period is a user name and what
comes after the period is passed to the user's program as an argument, so
that a user can have his mail automatically processed according to what
address is used.  For example, I might want to have mail to "greep.unix"
filed in my "unix" folder, and mail to "greep.header-people" appended to
a file (say /dev/null).