Archiving your faxes: keeping proof of transmission in 2026

Short answer: a fax only has evidential value if you can produce, months or years later, three interlinked items: the document exactly as it was transmitted, the time-stamped transmission report showing the number dialled and the page count, and a trace of the sender's identity. Keep the whole set for the limitation period applicable to the matter — 5 years for most civil and commercial obligations, 10 years for accounting records, 20 years for a medical file. The safest format remains a non-editable PDF accompanied by the exported transmission log, all of it in a folder structure that someone other than you can read. An online fax service provides these items natively; a paper fax machine, almost never.

The scene always plays out the same way. Eighteen months after the fact, one party disputes ever having received the document. You start looking. You find a photocopy of the cover page, with no date. The fax machine's log has been overwritten — it only kept the last fifty transmissions. The assistant who sent the fax has left the company. The result: the fax really was sent, everyone is convinced of it, and nobody can demonstrate it.

We covered the legal standing of the fax in detail in our article on the legal value of the fax in 2026: it rests on freedom of evidence and the court's sovereign assessment. But that freedom has a brutal corollary: it is up to you to provide the material. Sloppy archiving cannot be fixed after the fact.

What actually constitutes proof of a fax

A transmission report on its own proves very little: it attests that a T.30 exchange completed successfully between two devices at a given time. It says nothing about the content. Conversely, a PDF of the document with no record of transmission only proves your intention. Evidential weight comes from the assembly.

The four pieces of the file

The third point is underrated. An isolated report can be suspected of fabrication; a continuous log, in which the disputed transmission appears between two other sends unrelated to the matter, is far harder to challenge. That is the argument from the series: nobody falsifies an entire history for the sake of one file.

The TSI header, the forgotten signature

The T.30 protocol carries a TSI field (Transmitting Subscriber Identification): the character string your equipment announces to the receiver, reproduced in the header printed at the top of every page received. If that field is empty or generic, the recipient gets a document with no identifiable origin — and you lose a link back to yourself. Check that it contains your fax number in international format and, ideally, the name of your organisation. It is a two-minute setting in most interfaces, and it carries over to all your future transmissions.

How long to keep records

There is no such thing as a "fax retention period": there are periods attached to the nature of the document transmitted and the associated legal risk. The fax is only a vehicle.

The applicable benchmarks

• Accounting records and supporting documents: 10 years from the close of the financial year (article L.123-22 of the French Commercial Code). A purchase order, an invoice or a credit note sent by fax follows this rule.
• Civil and commercial contracts: 5 years, the general limitation period (article 2224 of the French Civil Code). Many departments prudently align all contractual exchanges to 5 years.
• Employment and payroll documents: 5 years for payslips, 3 years for certain filings, according to the schedules published by the ministère du Travail and reproduced on service-public.fr.
• Medical file: 20 years from the last visit, under article R.1112-7 of the French Public Health Code — with special cases for minors and deceased patients. Reports faxed between practitioners fall within the scope of the file.
• Public procurement and planning: 5 to 10 years depending on the document; litigation appeal deadlines often determine the useful retention period.
• Notarial deeds and formalities: long-term retention, managed by the notary's office, but the agency or company that sent the document is well advised to keep its own copy for 5 years.

One simple principle to settle the question: keep the proof of transmission for as long as the document itself, never less. A purchase order kept for ten years whose proof of transmission was destroyed after one year creates an awkward imbalance in litigation.

The opposite constraint: not keeping records too long

The GDPR imposes storage limitation (article 5(1)(e)). Keeping "everything, forever" is not a cautious stance, it is a breach. We expanded on this in our article on fax and the GDPR: each category of fax must have a defined retention period in your record of processing activities, and must be effectively deleted when it expires. A fax containing health data or an identity document kept for eight years "just in case" is a risk, not a safeguard.

The three pitfalls of real-world archiving

The log that overwrites itself

An office fax machine keeps between 30 and 200 transmissions in memory depending on the model, then overwrites the oldest. Many organisations discover this limit the day they go looking for a transmission from last year. If you still use a physical device, print or export the log at fixed intervals — monthly at a minimum — and file it. The same reasoning applies to networked multifunction printers, whose internal drive is often wiped during maintenance work.

The PDF that isn't the one that was sent

A classic mistake: archiving the source file (the .docx, the spreadsheet) rather than the PDF actually transmitted. Between the two, an update, an automatic date field, a substituted font — and the document produced in court no longer matches the one the recipient received. Always archive the final rendering, the one whose pages were counted in the report.

Single-location storage

A folder on the executive assistant's machine is not an archive. The common-sense rule, the one recommended by ANSSI guidance on backups, remains redundancy: at least two copies on separate media, one of them offline. For modest volumes, an encrypted external hard drive is more than enough; for organisations archiving years of document flow, a two-bay NAS enclosure offers internal redundancy and controlled network access. The key point is that the backup copy must not disappear along with the machine used to send the fax.

Building a folder structure that outlives its author

An archive only has value if someone who wasn't there can find the item in five minutes. That comes down to the naming convention.

A naming scheme that holds up

2026/
  10/
    2026-10-02_FAX-OUT_mairie-sens_DIA-12-rue-des-lilas/
      document.pdf
      rapport-transmission.pdf
      page-de-garde.pdf

Four rules are enough:

1. Date first, in ISO format (2026-10-02): alphabetical sorting becomes chronological sorting.
2. Direction of transmission (FAX-OUT / FAX-IN): after two years, received and sent get confused very quickly.
3. Recipient in plain language, not just the number.
4. File reference, the one already used in your business software.

For inbound faxes, the logic is identical: the notification email serves as proof of receipt and must be archived along with its attachment, not merely "read then deleted". Our fax-to-email guide covers the configuration of aliases and forwarding.

Scanning properly whatever still arrives on paper

If some of your faxes land on a printer, scanning becomes the weak link: a cover page photographed at an angle with a phone does not constitute a serious archive. A document scanner with an automatic feeder produces straight, multipage PDFs that can be searched in full text, at a negligible cost relative to the hours saved. Organisations receiving a lot of thin or stapled documents also benefit from a manual paper trimmer to cleanly remove edges and punch holes before feeding.

Do you need qualified time-stamping?

This is the question legal departments ask, and the answer is nuanced. The European eIDAS Regulation (No 910/2014) defines qualified electronic time stamps, which benefit from a presumption as to the accuracy of the date and the integrity of the associated data. That level of assurance is useful for documents whose date determines the right: filing within a cut-off deadline, responding to a tender, exercising a right of pre-emption.

But qualified time-stamping applies to a file, not to a transmission. It attests that this PDF existed at a given second — not that it was received. For proof of transmission, the pairing of "transmission report + continuous log" remains the central item. The two combine well: time-stamp the PDF before sending if the date the document was created matters, then archive the report for the date of transmission.

In practice, three tiers cover almost every case:

The register of sensitive transmissions

Organisations that are strongest in litigation do not owe that advantage to software: they keep a register. One line per sensitive transmission, filled in at the time of sending — never reconstructed afterwards.

The useful columns: date and time, sender, recipient and number dialled, nature of the document, file reference, page count, status, archive location. A shared spreadsheet does the job for a few dozen lines a month. Departments that prefer paper for critical items use a numbered carbon-copy register, whose continuous numbering makes any later insertion visible — an argument appreciated during an audit.

This register also helps day to day: it lets you answer "we never received it" in thirty seconds without digging through mailboxes. For multi-site organisations, it can be broken down by branch, following the logic described in our article on organising faxing across multiple sites.

And when you have to produce the evidence

The day you are asked for proof, pay attention to how you present it:

• A single reconstituted PDF in this order: cover page, document, transmission report, log extract.
• A broad log extract, covering the whole day rather than just the relevant line: the series is what creates credibility.
• No editing. A report that has been cropped or retyped instantly loses its value. If anonymisation is needed (other recipients appearing in the log), redact with a solid block and state it explicitly.
• An internal attestation signed by the manager describing the archiving procedure, where volumes are large. It does not prove the transmission, but it explains to the court why your evidence is reliable.

For files kept in paper form, a rigid lever-arch file with dividers by quarter prevents documents from scattering — trivial, but it is exactly what's missing on the day of the hearing.

Frequently asked questions

Does an "OK" transmission report prove receipt?

It proves that the remote fax machine acknowledged receipt of the pages at the T.30 protocol level. It does not prove that a human read the document, nor that it reached the right desk. That is why case law treats the fax as the beginning of proof that needs corroborating: a noted follow-up phone call, a follow-up email or a reply from the recipient considerably strengthen the file.

Can you destroy the paper after scanning?

Yes, subject to conditions. Article A.102 B-2 of the French Tax Procedure Code governs the scanning of paper invoices: identical reproduction, PDF with a hash, and storage on a medium guaranteeing integrity. Outside the tax field, the NF Z42-026 standard describes good practice for faithful digitisation. In practice: scan properly, document your procedure, and keep the original for instruments where paper form is required.

How long does an online fax service keep my transmissions?

It varies, and it is a question to ask before committing. Some keep them for 30 days, others for several years. Never make your legal retention dependent on the provider's retention policy: export your logs and PDFs regularly to your own archive. An automated monthly export to a dedicated folder settles the matter for good.

Should received faxes be archived like sent ones?

Yes, and this is often the weak spot. An inbound fax can be just as binding as an outbound one: a formal notice, a notification of a deadline, a summons. Keep the notification email with its headers and the attachment, and record the actual date of receipt in your register.

What if I've lost the report but kept the document?

All is not lost. Ask your carrier or provider for an extract from their own technical logs: retention periods on the provider side are sometimes longer than yours. Failing that, build a body of evidence: an itemised bill showing the call, email exchanges, a note in the file. The court assesses the whole.

Key takeaways

• Proof of a fax is an assembly: transmitted document, time-stamped report, continuous log, sender identity.
• The retention period follows the nature of the document, not the channel: 5 years in general, 10 years in accounting, 20 years for a medical file.
• The GDPR forbids keeping everything indefinitely: set a period per category and delete on expiry.
• Archive the PDF actually sent, never the source file.
• Two copies minimum, one of them offline, and a naming scheme a third party can read.
• Qualified eIDAS time-stamping complements proof of transmission; it does not replace it.
• Export your logs yourself: never rely on your provider's retention policy.
• A register kept in real time beats any after-the-fact reconstruction.

To check coverage for a country before sending a fax intended to be archived, see the list of compatible countries; answers to specific cases are gathered in the FAQ.