What is “TSID”?

Last Update: August 9th, 2021


TSID stands for “transmitting subscriber identification.”

It identifies the specific fax machine sending a fax.

It is very similar to “CSID” (called subscriber identification), which identifies the fax machine receiving a fax.


TSID is a type of metadata that accompanies a fax transmission. It contains the sending fax machine’s fax number and name (usually the name of the person or company the fax belongs to).

The TSID information appears printed on the header of a fax along with the date and time of the transmission. The receiving fax machine will store TSID information in its fax logs.

Fax logs with TSID records can be compared with phone call records to authenticate a transmission at a later date.

How to change, configure, or set up TSID on a fax

TSID is programmed into a fax machine. If the fax machine moves to a different fax number the TSID information will need to be updated.

In some models of fax machine, if power is interrupted to the machine, TSID will need to be reprogrammed.

Consult your instruction manual. Each fax machine will have different settings.

  • With an online fax service, only the TSID name (and not the number) will need to be configured.
  • On a standalone fax machine the “options” or “settings” button will have the TSID settings. Use the keypad to enter both the TSID number and the
  • Connected fax machines may be able to update the TSID using standalone or software methods.
  • On a fax modem, look for TSID settings in the modem’s software or driver.