Auto mail bouncer for testing

[Edward Dekkers]

Quite often, my customers want to test their mail set-ups on-site. Many 
of them do not want to simply send a message to themselves. If they have 
their own mail server, this is not a real test, and if they don't it 
only proves their ISP's mail server is returning their mail. Most want 
the mail to travel a few hops and then come back.

Is it possible to set up a specific user, or maybe get it to react on a 
certain subject line (or both) to set up sendmail (procmail?) to send a 
message back to an originating address for testing?

For example, I'm on site and want to test e-mail.

I send a message on the customer's PC on site to mailtest at mydomain.com 
with subject "MAILTEST", and based on the e-mail coming in to my mail 
server, have the server check for one or both of those conditions (via 
procmail?), then send and e-mail back to the originating address back 
say for example "This is the mail server at mydomain.com. You have 
requested a mail test. The test was successful. Here is a copy of the 
mail you have sent:"

etc. etc. etc.

Or is somebody doing this already with an easy to remember URL?

Regards,
Ed.

BTW. procmail looks scary. I guess if I have to I have to but some 
suggested reading that I can understand would be appreciated.