I'm having an issue with a FAX passthrough configuration, from time to time and with certain external FAX machines more than with others.
We assume that the external FAX machine is connected directly to the POTS or via a classic PBX.
When our internal FAX machine is also connected through a classic PBX, it can send FAX without any problem all the time.
On the other side, when it's connected via the FXS port of a LinkSYS SPA3102, itself linked to a FreePBX IP-PBX which is hooked into the POTS via a XORCOM XR0055 interface, then it doesn't manage to send a FAX to that specific external machine, while it may be able to send to other external FAX machines.
Any ideas why is that so and how to solve it?
FreePBX 18.104.22.168 and Asterisk 1.4.36