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Call it from an ordinary voice phone. A working fax machine answers and plays the fax handshake: a regular beeping, then a hissing screech as the two machines negotiate. If you hear a voicemail greeting, a human voice, or endless ringing, it is not a working fax line. That one call is the fastest test there is, and it costs you nothing.
When you call a fax number and a machine picks up, you will first hear a steady beeping tone. That is the calling signal. Then comes the handshake: a burst of hissing and warbling as the machines agree on speed and settings. It sounds strange, but it is exactly what you want to hear. Hang up once you recognize it; you have your answer. If the line answers and you hear silence, a recorded human greeting, hold music, or a modem screech that never settles into the fax handshake, that line is not ready to receive your fax.
| What you hear | What it means | Next step |
|---|---|---|
| Beeping, then a hissing handshake | A fax machine answered. The line works. | Send your fax. |
| Voicemail greeting | Voice calls and faxes share the line, and voicemail grabbed it first. | Call the recipient and ask for the dedicated fax number. |
| A person answers | Not a fax line, or the machine is set to manual answer. | Ask them to switch the machine to receive, then send. |
| Rings with no answer | Machine off, unplugged, or the number changed. | Confirm the number with the recipient before trying again. |
| Fast busy signal | The number is disconnected or out of service. | Do not send. Get a current number. |
Send a one-page test fax with a cover sheet that asks the recipient to confirm receipt by phone or email. If it goes through, the number works and you have proof. Some online fax services publish test numbers you can fax for free to check your own setup in reverse. Your own machine's transmission report is another source of evidence: "no answer" and "busy" errors tell you the remote end never picked up, while a "line error" after several pages suggests the number works but the line dropped mid-send.
Fax numbers get disconnected like any phone number. Offices consolidate lines, switch to online fax, or change carriers and forget to tell everyone holding the old number. Another common case: the fax machine moved behind a new phone system, and the old direct number now rings a receptionist or a voicemail box. If a previously reliable number suddenly fails, assume the setup changed on the other end and ask for the current fax details rather than redialing all week.
Toll-free fax numbers (800, 888, and similar in the US and Canada) behave like normal numbers for testing; the voice-call trick works the same. For international fax numbers, dial exactly as you would a voice call, including the exit code and country code. Keep in mind that LetterAgent sends faxes to US and Canadian numbers only, and its fax service is currently in testing.
Ready to fax it? Fax with LetterAgent: describe it to your AI assistant, approve the exact quoted price, and it is sent.
LetterAgent is a working name. Prices include print, postage, and our service fee. US prices in USD, Canadian prices in CAD (Canadian prices exclude applicable sales tax, added at checkout). Currently in private testing.
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