The law
A transmission report attests that an identified machine answered and acknowledged the document. An email only proves that a message left a server.
Understanding fax
What a fax really is, and why it is still here
Fax did not survive out of nostalgia. It survived because it produces a proof that neither email nor a web form can produce. Here is what happens on the line, and what it changes legally.
Short answer
A fax sends the image of a document from one machine to another over the telephone network. The sender gets a report stating that the receiving machine answered, accepted and acknowledged every page. That acknowledgement, not the content, is what gives it evidential weight.
What happens between the click and the report
Four operations separate the upload from the delivery receipt. None of them is visible on screen.
- 1
Upload
The PDF leaves the browser over an encrypted link. It is never printed: its vector content is read directly.
- 2
Rasterisation
Each page becomes a pure black-and-white image, no grey levels, at the definition fax machines expect.
- 3
Line negotiation
The gateway calls the remote machine and agrees on speed and error correction mode before a single page moves.
- 4
Transmission report
The remote machine acknowledges each page received. The report records the time, the duration and how many pages were accepted.
The facts, in six lines
| Transmission protocol | ITU-T T.30 / T.38 |
|---|---|
| Sending definition | 204 × 196 ppp |
| Accepted format and size | PDF — 10 Mo |
| Usual delivery time | ≈ 5 min |
| Destinations covered | 12 |
| Prefixes listed | 60 |
Why it has not disappeared
Three professional worlds still insist on it, and each has a different reason.
Healthcare
Exchanges between practitioners often travel outside open mail systems. A phone line stays a closed channel, with no intermediate storage.
Public administration
Court registries, benefit offices and prefectures keep written procedures that name the fax. Until the text is rewritten, the channel stays mandatory.
Practical guides
Sending a fax over the internet: the four methods
Web service, email gateway, carrier option or an adapter box: what each method costs, what trace it leaves, and which use it actually suits.
Faxing from a smartphone, without an app
Scan cleanly, get the contrast right and transmit from a mobile browser — no app required, on Android as on iPhone.
Sending a fax without a machine: who does the machine's work
The machine is no longer needed at the sending end: what it used to do, what does it instead, and what its absence really changes for a sensitive document.
Sending a fax from a computer: what each system can do
Windows, macOS and Linux each have their answer to faxing — and two of them assume hardware that has become impossible to use. What still works, and why.
Sending a fax from Gmail: what Google does not do
Gmail does not send faxes. The three ways around it, what each one costs, and the two lasting copies an email gateway leaves behind.
Fax cover sheet: what it must say, and what it must not
The four entries that make a cover sheet useful, what must never appear on one, and why the page count matters more than everything else put together.
Virtual fax number: what you rent, and what you do not own
The four things to check before subscribing, and the one no offer advertises: what becomes of the number the day you stop paying.
Sending a fax to several recipients: one send per number
A fax has no carbon copy field: reaching several recipients always means repeating the send, with a separate cover sheet for each one.
Sending a fax from Outlook: the address book and its illusions
Outlook does not send faxes. The three possible routes, and why a number picked from the address book is not a verified number.
Sending a fax abroad: dialling right, and choosing who carries it
Dialling a foreign number correctly, and choosing a service that actually reaches the destination — two separate questions, routinely conflated.
Receiving a fax: what it takes, and what this service does not do
Virtual number, router option or a classic machine: what receiving requires, what it costs, and why this service only sends.
Fax by sector
Fax in healthcare: who still uses it, and why
Practices, laboratories and hospitals still exchange faxes. What the health-data regime changes, and what to verify before transmitting.
Fax in the legal world: proof before speed
Registries, lawyers and bailiffs use it for one precise reason: the report attests that an identified machine accepted the document at a given time.
Fax in public administration: where it is still provided for
Prefectures, benefit offices and tax services still accept it. Where procedures still provide for it, and how to verify the number before transmitting.
The technical side
T.30: the conversation two fax machines hold before exchanging anything
The standard behind every exchange between two fax machines: how they identify each other, agree on a speed, and confirm each page received.
T.38: why analogue fax fails over IP, and what repairs it
Why an analogue fax machine fails on a voice-over-IP line, and how T.38 restores reliable delivery by carrying the protocol rather than the sound.
Fax resolution: what each mode actually changes
The three standardised definitions, what they change for legibility and call duration, and which one suits the document being sent.
Accepted file formats: PDF, and nothing else
A fax is a bitonal image: every file is rasterised before sending. Why this form takes PDF only, and what the conversion loses along the way.
Fax transmission time: what really determines it
How long a fax takes depends on the initial negotiation, the agreed line speed and the density of the image — far more than on page count or file size.
Fax and fibre optic: why transmission breaks part-way through
A fax is modulated sound built for a switched line. Over fibre it crosses a voice codec that distorts it, so sending breaks mid-transmission.
Fax and internet box: why the phone port is not a line
The phone port on a router is not an analogue line but a gateway. What to disable on the box so that a fax machine still gets through.
Fax security and encryption: a reputation without a protocol
The T.30 protocol provides no encryption at all. The fax's reputation for security came from the switched line, not from cryptography.
Why a fax fails to go through: the causes, by frequency
Number format, a remote machine that no longer answers, an oversized document, or a line converted to voice over IP: what actually blocks delivery.
Frequently asked questions
- Does a fax hold legal weight?
- The transmission report is a starting point of proof: it establishes that an identified machine accepted the document at a given time. Its force then depends on the court's assessment and on the rules that apply to the case.
- Do I need a fax machine to send a fax?
- No. An online gateway replaces the hardware: it converts the file and places the call on your behalf. Only the receiving end still has to be a fax machine, physical or virtual.
- Does fax still work over fibre?
- An analogue machine plugged into a fibre router often fails, because voice travels in packets. Going through an online gateway avoids the obstacle, since the call starts from the operator network rather than the home.
Send a fax now
The form fits on one page: a PDF, a recipient and a return address. No account, no card.
Open the form