It is possible to write a Formativ applet that creates a GroupWise rule. See the GroupWise online Tokens Reference (A – Z) here.
Unfortunately, there does not seem to be way to set up a rule that automatically prints a message.
Alternatively, you could write an applet that executes on message arrival, checks for the required conditions, and prints the message data. For this you could use the ItemPrint() routine in the GroupWise Token API, or else develop your own printing method and format.
Unfortunately, ItemPrint() displays the Print Item dialog in GroupWise. It doesn’t print anything, and requires manual user intervention to start the actual print process. This probably eliminates it as a potential solution.
The only way you could currently get this to work would be to write your own printing functionality (perhaps automating the application associated with the attachment in question).