I recieve all the undeliverable reports for mailings sent from my company. Moving and cataloguing them can take a while, and it would be handy if I could create a rule that did that for me.

The most robust way of doing this would seem to be to run a rule based on the Undeliverable message class. However, I can't see message class as an option anywhere in the advanced rules wizard, and Googling it is no help.

EDIT: I already have a rule that searches for "Undeliverable" in the subject header of emails received and moves them, but this only affects traditional emails (i.e. those with a message class of "Message") and ignores actual undeliverable reports.

Am I missing something obvious, or can this not be done?