What type of fax relay is supported by the Right fax card ?
i assume t38.
So you may have a voip dial-peer with t38 enabled for the fax DIDs pointing back to fax server ? If yes you can try configuring a POTS dial-peer with the same destination-pattern, map the FXS port where the fax machine is and use a preference of 1. Default dial-peer preference is 0. So voip dial-peer will always be used and fax will go to rightfax server. If the voip dial-peer gets a busy, it should hunt to the pots dial-peer and all fax should receive on the analog fax machine.
Let me know if that works, by rating the post!
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus