Number of Pages
This is the most impactful factor in fax transmission time. The more pages you send, the longer the transmission time and time to get a confirmation.
Document Size
No matter what you are sending or what type of fax machine you send it through, online or traditional, the volume of data you transmit matters. This is because different document types will be of different file sizes. A simple text document will have the fastest transmission time, while something very image-heavy will take longer. This is important to remember when trying to estimate how long a fax will take to send. The same also applies to receiving a fax.
Phone line
Bad phone connections are to blame for many lost or unsent faxes. Documents may fail to transmit completely if the dialed line is busy or gets disconnected. You can verify if a fax line is working and available to receive a fax by calling the fax number. If you get a busy tone the fax line is not currently available to accept a fax, you can try again later. If you hear the dial up tone the fax line is active and ready to accept a fax.