The first step in testing is to send some pretend mail through mdforward. Save some items of real mail you've received, and then feed them one at a time to mdforward:
% bin/mdforward < message1 % bin/mdforward < message2
Then see where they were delivered. (For a start, using a single .mdforward/default file that delivers to a Mailbox is easiest.) Check the log file too for errors.
Once the most basic setup is handled, add some non-default users. When this seems to be working, try forwarding mail to some account on another server (typically, your dialup account).
With all this offline testing looking OK, it is time to turn on mdforward for real mail. This is done by editing your .forward file to look something like this:
\giles, "| /home/giles/mdforward-1.1/bin/mdforward"
The backslash and username are important. This ensures that mail is delivered as usual, so you can check that mdforward is doing the right thing during testing. Once you've finished testing the \username should be removed. (That bit should probably be in <FLASH> it gets missed so often. Please remember!
If you deliver to procmail currently you may wish to continue doing this although sorting out which program forwarded what will be challenging. (Hint: mdforward always puts a Delivered-to header line in mail that is forwarded.)
When you're finished testing, please remember to take out any \username from your .forward file that you created or your mail will be delivered twice, once by mdforward and once by sendmail.
Last (but not least!) please let me know that you're using mdforward, and if you'd like to be notified about updates. Thanks!