I configured iaxmodem and hylafax for on of our customer last week. I test FAX with sending fax internal extensions and everything worked prefect.
But today they called me and said they have a problem in sending and receiving FAX ! Again troubleshooting !
I checked out log file log file was :
SEND FAILED: JOB 4 DEST 88276650 ERR  No receiver protocol (T.30 T1 timeout)
I googled about this problem and there was no direct answer to this. someone said there is a problem on connection your device and you have some thing like “UDP being a lossy medium”.
Anyway after question from friends problem solved with changing Tenor configure:
#set FaxRelay G.711 Mu-Law
If you have a same problem set FaxRelay to Mu-Law maybe cause to solve yours.