How do you fax to an extension number?

To fax to an extension number, you need to insert a pause into the number you fax to. This is done in different ways on different fax machines, and can be found in the manual. It may be done by hitting the comma or period buttons, or by a dedicated pause button on the fax machine. This pause allows the call to go through and the extension service to ask for the extension you want to send the fax to.

For example, at my work we have a Brother 2820 Fax machine, with a button that says Redial/Pause on it. If I needed to fax to (555)-555-5555 at the extension 555, I'd dial 1555555555 then hit my pause button twice to insert two pauses to wait for the extension service, and then dial 555, and finally hit start to send the fax. This would dial the number, then wait for a few seconds for the extension service to ask for an extension, then dial the extension.