A fax that fails
Why a fax fails to go through: the causes, by frequency
Four causes account for the vast majority of failures. They are unrelated to one another, and none is fixed in the same place.
Short answer
In order: a malformed number, a remote machine that does not answer or is no longer a fax, a document the gateway refuses, and a line converted to voice over IP at the receiving end. The first three are fixed on the sending side; the fourth is beyond the sender's reach.
Number format, cause number one
A national number written with its leading zero behind an international prefix reaches no one. Conversely, a foreign number dialled without a prefix goes to a domestic subscriber who never asked for it. Check the format the target country expects before anything else: it is the most frequent failure, and the most silent.
The remote machine has changed nature
Many numbers published as fax numbers have become voice lines. The call connects, a person or an answering machine picks up, and the negotiation fails for want of a counterpart that speaks the protocol. The report then shows a negotiation failure, not a busy line — and that distinction guides the diagnosis.
The document is refused before the call
A file that is not a PDF, a password-protected PDF, or a size beyond the limit are all rejected before any dialling. The failure is then immediate and consumes no attempt: if the refusal arrives in under a second, the cause lies there and not on the line.
The recipient's line runs over IP
This is the cause the sender can do nothing about. An analogue machine wired to a router undergoes compression designed for speech, which distorts the modem's tones. Attempts fail irregularly — sometimes one page gets through, sometimes none. Only the recipient can remedy it.
Frequently asked questions
- How many attempts are made before giving up?
- A busy line triggers several spaced retries. A refused document or an invalid number, by contrast, are never retried: repeating the same attempt would reproduce the same failure.
- The report shows a failure with no clear reason — what now?
- Recheck the number format, then confirm with the recipient that the machine is still a fax. Those two checks cover most cases; beyond them, the cause is almost always on the receiving line.
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