My first thought would be to check ISP to see if they offer alternate 'throw away' ids. These are often used for responding to ads, but could be useful here. You could embed identity into templates, but that works only if recipients always respond in HTML. If this is a server where you have full access, I suggest creating forwarding addresses that forward to info@domain.com.

I guess I was wrong. We all send mail via IMAP from info@domain.com. I need to know which machine sent the message. When previously received a response to The Bat program on our message from machine 1, the recipient was info@domain.com - machine 1, so I was able to identify the sender, but if I set this in TB as the reply address, the recipient will enter as the reply as address info@domain.com - machine 1, which of course does not work.

Other than setting forwarding addresses from the server, all I can figure would be setting the email such that you could identify it on return. A possibility: set actual address in 'reply to', using dummy address for FROM. OR... put identifying information in signature and in letter include a statement such as 'reply above this line' to encourage people to leave message intact on replies. ANOTHER option to try would be setting FROM address to "Info machine1" info@domain.com , but that relies on your ability to sort returns from that, which may require additional tools. Anyway, those are my best ideas. Another support person may see this and offer better ideas, but I'm tapped out. All the best in your pursuits on this.