Assuming you want a poster rather than subject based filter, surely you need to study the headers of the complete message set and check if there is the same or reasonably similar header with an obvious pattern across the set (e.g. FQDN)? Depending on which header item it is, it might then be possible to compose a rule if Usenapp can be changed to allow users access to more header items than at present. I hope that makes sense!
