Customer has 7400 system Version 4.98 using SIP trunks.
Trying to use SL ports for incoming and outgoing faxes.

This is a school with perhaps 10 fax machines.
Trying to save POTS line charges.

SL ports work OK on incoming faxes
Outgoing faxes get "communication errors" consistently.
Fax machine spped lowered to 9600, doesn't help.

SL ports are set up as fax3 and CO ringing.
Codec for SIP trunks is set for G.711U

I'm told these settings are correct.

Anyone have a solution ?