When I try to send to two addresses I get an error in the filter file malformed address: , [[email protected]](mailto:[email protected]) may not follow [[email protected]](mailto:[email protected]). What is going on?

Have you got

deliver "[email protected], [email protected]"

in your filter? If so, that is your problem. You should have

deliver [email protected]
deliver [email protected]

Each deliver command expects just one address.