exten => fax,1,SetVAR(FAXID=${UNIQUEID})
exten => fax,1,SetVAR(FAXFILE=/var/spool/asterisk/fax/${FAXID}.tif)
exten => fax,2,rxfax(${FAXFILE})

exten => h,1,GotoIf($["${FAXFILE}" : ""]?:99) ; on hangup, was there a faxfile?
exten => h,2,SetVAR(CALLFILE=/tmp/${FAXID}.fax)
exten => h,3,system(echo "Channel:ZAP/g1/${TODIAL}" >${CALLFILE})
exten => h,4,system(echo "MaxRetries: 0" >>${CALLFILE})
exten => h,5,system(echo "WaitTime: 20" >>${CALLFILE})
exten => h,6,system(echo "Application: txfax" >>${CALLFILE})
exten => h,7,system(echo "Data: ${UNIQUEID}" >>${CALLFILE})
exten => h,8,system(mv ${CALLFILE) /var/spool/asterisk/outgoing)