Sendmail configuration

[Bob Bell]

Can anyone point me to information on the use of "+" in address with
sendmail (as in "bbell+extrainfo at domain.com")?  I don't know what it's
called, so it's rather hard to google for.  Or perhaps someone has
a ready-made solution to my problem?

Basically, I want to track the "envelope" destination of the message.
I've got this somewhat working by putting lines like "rjbell4:
bbell+rjbell4" in my aliases file.  This somehow sets $1 in my
procmailrc, though I'm really not clear on how that gets done.  The two
problems with this approach are (1) double indirection (e.g., postmaster
-> root -> user ) only keeps the context of the last alias, and (2)
I don't get $1 for a non-aliased account (if I add "user: user+user",
then $1 will *always* be "user").

Do anyone have any suggestions?  (And no, moving to another MTA really
isn't in the cards in this particular case)

-- 
Bob Bell
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 "We all know Linux is great...it does infinite loops in 5 seconds."
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