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From: nsb@THUMPER.BELLCORE.COM (Nathaniel Borenstein)
Newsgroups: comp.soft-sys.andrew
Subject: Re: Automagically adding headers to outgoing mail?
Message-ID: <Uc9K4720M2YtI2g6F4@thumper.bellcore.com>
Date: 6 May 91 13:58:31 GMT
References: <1991May04.032724.11127@convex.com>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 12

You can use the init file mechanism to set up a new menu that adds a
Reply-to header field before sending the mail.  Something like this
should do the trick:

addmenu sendmessage-compound-operation "Send W/Reply-To" sendmessage
sendmessage inherit "sendmessage-add-header Reply-to: nsb@bellcore.com;
sendmessage-send-message"

This belongs in your .messagesinit AND .sendmessageinit files, if you
ever run the program under both the names "messages" and "sendmessage". 
What I do is I have both of those init files include another file called
".amsinit" that has all the lines I want to use in both.