Short answer
The most common causes are a wrong number or one that is not a fax, a busy line, a recipient fax machine that is switched off or out of paper, and a line switched to voice over IP that distorts the signal. Your fax status, tracked in real time, shows the failure; check the number and try again.
The most common causes
A wrong number, or one that is not a fax number: this is the leading cause. If a person or an answering machine picks up, the fax cannot go through. Next come a busy line or no answer, then a recipient fax machine that is switched off, jammed or out of paper.
More recently, many failures come from lines switched to voice over IP: internet routers compress voice for the ear, which damages the fax's modem signal. This is a problem on the recipient's side that the sender cannot fix.
What you see on the status page
The status page shows whether the fax is queued, being sent, sent or failed. A failure is not charged for, since nothing ever is, and uses up no credit: you can correct the problem and send again.
What to do
First check the number, digit by digit, against a recent document from the recipient. Then try again a little later: a line that is busy at 9 am is often free by 11 am. If the failure keeps happening, call the recipient: they can confirm the number, check that their machine is switched on and has paper, or suggest another channel.
A very dense document — photos, coloured backgrounds — takes longer to transmit and is more likely to be cut off: a high-contrast black-and-white version goes through more easily.
Key points
- Leading cause: a wrong number, or one that is not a fax.
- Busy line, machine switched off or out of paper, unstable VoIP line.
- The real-time status shows the failure.
- Check the number, try again later, call the recipient.