Trying to send a fax, the device will give an error message which varies depending on the device model and producer.
Furthermore, deactivate the following settings:
- Note that a fax number dialed needs an prefix number (e.g. 9 for UK).
- Deactivate V.34
- Set the maximum bit rate to 9600 bps (alternatively marked as 9.6k)
- Deactivate the function "Use on extension.
- Decativate automatic telephone ringtone
- Deactivate automatic prefix number
- Enable port range 4000-4999 in your firewall
Check in the manual of your fax device, if the above mentioned settings are applicable for your fax and how to configure the settings. In case of doubt, ask the producer directly. Many manufacturers provide the configuration details on their website in the FAQ or Troubleshooting section. Pay attention to any note concerning sending faxes via VoIP.