Hi Stephen, Try sending the fax with the following format: "10 digit phone number * extension number" so it looks like:
This may not work depending on the receiving machine. You are sending to another number outside of RC, I'm not sure if the receiving system will recognize the " * " symbol, so you'll probably want to test it and follow up with a phone call to assure they received it.
Note: This will not work when sending to a RingCentral number. Faxes to RingCentral must be sent to just the 10 digit number.