If you are sending a fax manually and the line is busy, press Redial/Pause, wait for the other fax machine to answer, and then press Black Start or Color Start to try again. If you want to make a second call to the last number dialed, you can save time by pressing Redial/Pause and Black Start or Color Start.
Redial/Pause only works if you dialed from the control panel.
If you are sending a fax automatically and the line is busy, the machine will automatically redial one time after five minutes.