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Fax Routing Extension

Fax Routing Extension: What Is It?

Fax Routing Extension

Reaching a specific person or department behind one shared fax number, and the simple dial-string method Fax.Plus actually uses to do it.

Published on
September 9, 2026
Last updated on
September 24, 2026

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  • A fax routing extension directs an incoming fax to the right person, department, or mailbox behind one shared fax number.
  • Some legacy fax systems used sub-addressing, a signal sent during the fax call itself, to route a fax this way.
  • Fax.Plus uses pause characters and an extension added to the dialed number instead of a protocol-level routing signal.
  • Up to 10 pause characters can be added to a number, each holding the line one second before the extension digits dial.

What Is a Fax Routing Extension?

A fax routing extension directs an incoming fax to the specific person, department, or mailbox behind one shared fax number, the same idea as dialing an extension on a phone system instead of reaching the main line.

Sub-Addressing, the Legacy Version

Some fax servers support sub-addressing, an optional signal sent during the fax call itself that tells the receiving system which extension to route the fax to, a routing concept similar to how identifying which number was actually dialed lets a phone system route a call. Fax.Plus doesn't rely on this signal.

How Fax.Plus Routes to an Extension

Instead, entering a destination number in Send Fax can include an asterisk (*) for each one-second pause, followed by the extension digits, for example +16692001010****5 dials the main number, waits four seconds, then dials 5. Up to 10 pause characters are supported. It's a dial-string technique, not a protocol-level routing signal, and it works whether the person managing routing for the account sets it up for a shared line, or it simply reaches a dedicated number for one person instead.

A Common Case: One Number, Many Desks

A small back office shares a single fax number across several desks, and reaching one specific person used to mean the front desk relaying every incoming page by hand. Dialing the main number, then a short pause, then that person's extension gets a fax straight to the right desk without anyone in the middle having to sort it first.

FAQs

How do I send a fax to a number that has an extension?

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Add an asterisk (*) to the number for each one-second pause needed, then the extension digits, for example +16692001010****5. Up to 10 pause characters are supported.

Does Fax.Plus use sub-addressing to route faxes to an extension?

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No. Some legacy fax systems used sub-addressing, a signal sent during the call itself. Fax.Plus instead uses pause characters and extension digits added directly to the dialed number.

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