You can control it from the Fax Console which can be opened from:
To cancel faxes from being sent out, go to the Outbox and delete the items that you want to Cancel.
To disable all faxes from being sent out:
Go to Fax Console (Click Start > All Programs > Accessories > Communications > Fax > Fax Console)
Click 'Tools > Configure Fax' to open the fax configuration wizard. Click Next two times
Remove the tick for 'Enable Send' on this screen. Click Next four more times. Click Finished.
Follow the above steps and place a tick for 'Enable Send' to restore sending fax.