[Asterisk-Users] Autodetecting faxes

[Asterisk]

I have managed to get spandsp working, and if I dial a specific 
extension I can receive faxes. WhooHoo.

However, I was wanting to use the "fax detect" option in order to allow 
individuals to receive faxes, but can't get that to work.

Given the following extensions (mainly copied from examples on the 
wiki), why is the call simply passed onto the sip device rather than 
being detected as a fax ?

Asterisk CVS-HEAD-02/02/05-07:11:04 built by asterisk on a i686 running 
Linux

Spandsp is 0.2pre9

Incoming lines are E1 line 30 channels PRI.

Many thanks.

Julian.

===============

exten => 442781,1,Goto(fax,1,1) ; dialling this number works
exten => 442781,2,Hangup()

exten => _4427XX,1,Answer() ; dialling any number in here does not
exten => _4427XX,2,Macro(dialsip,${EXTEN:3})
exten => _4427XX,3,Hangup()

exten => fax,1,Goto(fax,1,1)

[macro-faxreceive]
exten => s,1,SetVar(FAXFILE=/var/spool/asterisk/fax/${UNIQUEID}.tif)
exten => s,2,DBGet(EMAILADDR=extensionemail/${MACRO_EXTEN})
exten => s,3,rxfax(${FAXFILE})
exten => s,103,SetVar(EMAILADDR=jmls at tessera.co.uk)
exten => s,104,Goto(3)

[fax]
exten => 1,1,Macro(faxreceive)

exten => h,1,system(/usr/sbin/mailfax ${FAXFILE} ${EMAILADDR} \ 
"${CALLERIDNUM} ${CALLERIDNAME}")
exten => h,2,Hangup()