[Mimedefang] Where to put various tests?

[Nigel Allen]

Greetings

First off - to the author(s) of mimedefang - thank you! What a brilliant 
product - it has reduced the amount of spam we (and our customers) 
receive to almost nothing.

Of course - now we want to do more :)

I need to do the following and am not sure where within the filter I 
should put the logic.

If the sender is using an address from a given domain (internal) I need 
to extract a special x-header and see if if it's contents a) occurs in a 
text file or b) occurs as a folder in a given location.

If neither of these is true I need to reject the message with a reason 
for rejection and get them to re-send.

Should I do this in filter_sender or where?

Any tips / suggestions appreciated.

TIA

Nigel.