[incoming]

exten => s,1,Answer
exten => s,n,Wait(3)
exten => s,n,Dial(Zap/7,30,t)
exten => s,n,Hangup

exten => fax,1,Set(FAXFILE=/var/spool/asterisk/fax/${UNIQUEID}.tif)
exten => fax,n,rxfax(${FAXFILE})
exten => fax,n,Hangup