On Thu, 13 Nov 2003, Ben Coffman wrote:

> How would I make it so my sendamail could attach a footer to the bottom
> of each outgoing e-mail message.

From the authority:

http://www.sendmail.org/~ca/email/more.html

How do I add a footer/signature to all (outgoing) e-mails?
This is quite complicated. At first sight it might be simple: just "cat" 
some text (taken from a file or whatever) to the end of an e-mail passing 
through sendmail. However, there is a big problem: what is about 
structured e-mails, i.e. MIME e-mails? These can be arbitrarily complex 
and just "cat"ting a footer to the end of the body will break the MIME 
structure. Hence, there is no easy solution to this problem!

If you know enough about MIME and some C programming, then take a look at 
sendmail 8.11 and the libmilter/README. It now offers the functionality to 
achieve this goal. However, it is unsupported by me and sendmail.org! 
Please don't ask us questions about libmilter (however, we will fix bugs!)