My ancient mail server machine crapped out a few days ago. I cobbled together another machine from spare parts and the bone pile, which included reformatting the existing disk and installing a fresh copy of Windows 2000 (I've got lots of Win2000 licenses). This will be the internal SMTP server for the small company I work for.
The SMTP server for receiving mail for the domain, associated POP3 server, queuing system, and system that does some custom things including running scripts triggered by certain mail messages is our own software and does what we want. What I'm looking for is a means of sending mail to external addresses. This software needs to contact a DNS server, do the MX lookup, and send messages via SMTP to the various target systems. The internal interface to hand it mail messages can be just about anything, although most likely that will be via SMTP also. Free is fine, but I have no problem paying for such software if it does what I want without problems. However, any commercial software must have a trial period of at least 14 days because my experience is that there are a lot of gotchas and any software needs to be proven to work. If it works fine for 14 days I'm happy to pay for it.
I've tried a few free programs already, but each has its problems. One (don't remember the name) worked great but was limited to 10 messages/day although this was nowhere mentioned in the documentation. That really pissed me off, and I'd like to avoid that vendor. I wasn't entirely happy with the forwarding server in use before, so after 8 years or so it's time to look around again and hopefully find something better.
To summarize, here are the requirements:
Must run on Windows 2000.
Must NOT establish a server on ports 25 or 110, or must be configurable to avoid those ports.
Does not need security in accepting mail. It will be behind a router that will not expose its ports externally.
May be free or commercial. If not free, must have at least 14 day free evaluation period.
May use SMTP to receive mail to be forwarded, but may also require some alternate interface, like running a executable per message.
Does not need a queuing system, POP3 server, etc. Just needs to forward messages to MX machines of target domains.