Message tag suffix

I have written a program which manages the delivery of huge
mailing lists (ala majordomo), breaking the transmission into
bite-size recipient chunks which doesn't overwhelm the machine.

The script monitors a directory looking for a recipient and
message tag. I'm currently implementing procmail on this 
self-same machine, and now I need to pull "majordomo" lists
into this.

Is there a variable, similar to MSGPREFIX, that indicates
what tag procmail assigned during something of the form:

        :0 c
        backup

when it throws a message into the backup directory, with
a unique suffix?

Thanks.
---
Bob Gahl KD6KMX Bicycle (Ryan Vanguard) Mobile  ||      @
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