What is “EXT” on a Fax Machine?

LAST UPDATE: April 23rd, 2019


‘EXT’ on a fax machine is a port to plug in an extension telephone.

It is found near a ‘LINE‘ or ‘TEL‘ port which is used to connect the fax machine to the phone jack.


Fax machines and fax modems have an ‘EXT’ port to attach an extra phone or answering machine to the same line (and phone jack).

When a phone or answering machine is attached to the EXT port, it will function the same as if it was plugged into the same phone jack as the fax machine.

To use the EXT port:

  1. Make sure your fax machine is set up and working. It will need to be connected to a landline phone line.
  2. Using a phone cord, connect the landline phone to the EXT port on the fax machine.
  3. Use the landline phone as you would a regular phone.

An attached landline can also be used to check if the phone line is connected and has a dial tone.

Be aware that answering the phone handset when a fax is communicating will stop the transmission.

Similar Terms

Sometimes the “EXT” port is labeled “TEL.”

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