LetterAgent
Mail physical letters by just asking your AI assistant.
Home > Guides > Fax machine caller ID
Yes, as long as your phone line has caller ID service from the phone company. The machine's display shows the incoming number (and name, if provided) while the line is ringing, and most machines keep a log of recent callers you can scroll through later. Caller ID is separate from the fax header line printed on the page, which is typed in by the sender and can say anything.
On the machine's small LCD screen, during the ring cycle before it answers. If you share the line between a phone and the fax, you will see the number before the machine picks up, which is the whole point: you can tell a fax is coming. Most machines also store the last few dozen incoming callers in memory, listed with the date and time, and many print the caller information on the transmission or activity report. Some machines offer caller-ID-based blocking, so numbers you flag as junk are refused before they can send anything.
The most common reason is that caller ID is a phone-company feature, not a fax feature. If your line does not carry a caller ID subscription, the machine has nothing to display. This trips people up on VoIP adapters and some business PBX lines, where caller ID may be turned off or delivered in a format the fax machine cannot read. A few things to check:
This is the part that matters for identifying who really sent something. Caller ID comes from the telephone network and is based on the actual calling number. The fax header line (also called the TTI, transmit terminal identification) is programmed into the sender's machine by whoever set it up, and it can contain any name and number they typed. Junk fax senders have long known this: the header can claim to be anyone. If a fax's header number and the caller ID number do not match, trust the caller ID.
| Caller ID | Fax header line (TTI) | |
|---|---|---|
| Source | The phone network | Typed in by the sender's setup |
| Can it be faked? | Yes, but it takes effort (spoofing) | Trivially, just reprogram the machine |
| Shown where? | Machine display during ringing; call log | Printed along the top edge of the received pages |
| Required by law? | No | Yes, on every page in the US and Canada |
Online fax services keep their own transmission logs, and those usually include the originating number the carrier reported. Because the fax arrives as an email attachment or a dashboard entry rather than a phone call, you do not watch a display during ringing; instead you check the log or the cover data after the fact. When you send through LetterAgent to a US or Canadian fax number, the recipient's machine sees the call as coming from the service's sending number (fax is currently in testing, so availability is limited), and the page count is quoted up front before anything is sent.
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.
Need help? Ask your assistant: it can check a job's status any time. If it ever can't handle something: hello@getletteragent.com