This article provides information regarding the following error while attempting to send a fax:
[01/Oct/2019 13:22:48] Failed to send fax from '100' to '0958763727', because Received bad response to DCS or training.
Configure Fax using T.38 protocol
The error, as mentioned above, appears due to the reception of an unexpected message (bad response) when the bulk fax service asked for the remote fax machine's fax capabilities. Kerio Operator is not receiving a CFR (Confirmation to Receive) signal from the Provider side after sending the DCS (Digital Command Signal). The SIP flow diagram below shows this faulty behavior:
To resolve this issue, you need to contact your Provider, as some Providers may require Direct dial-in (dedicated) to send faxes. You can generate a Network trace (Packet Dump) while reproducing the issue. You can also Capture Network Communication using Packet Sniffer in Kerio Operator.