Short answer: in a dispute, a fax is only ever worth as much as its trace. Keep three inseparable elements — the document sent or received, the transmission report (number dialled, date, time, page count, status) and the confirmation email or provider log — in a stable format, ideally PDF/A, for the statutory period applicable to the document's content (often 5 or 10 years, sometimes 20 years in healthcare). Thermal paper fades within two to five years: it does not count as archiving.
This is the part almost everyone neglects. You wonder whether the fax actually went through, you check the acknowledgement, then you move on. Three years later, a tax audit, a dispute over a notice period or an insurance claim calls for proof of that transmission — and all that remains is a grey, illegible sheet in a binder.
What to keep: three items, not one
A properly archived fax isn't a file, it's a trio.
1. The document itself
The page sent or received, in full: cover sheet included, all pages numbered, header and footer visible. A document stripped of its cover sheet often loses any identification of the sender — and that is precisely what you will later be trying to establish. We set out the mandatory details in our guide to the fax cover sheet.
2. The transmission report
This is the centrepiece. It contains the number dialled, the date and time, the call duration, the number of pages transmitted and the status (OK / error / busy). On a physical fax machine, it's the ticket printed automatically. With fax-to-email, it's the confirmation email sent back by the platform.
A report reading "OK" does not prove the recipient read the document. It proves that a machine answered at that number, at that time, and acknowledged receipt of N pages under the T.30 protocol. That's already a great deal: in many rulings, the combination of report plus document has been enough to establish prima facie written evidence.
3. The provider-side trace
If you use an online service, your account history keeps a log that is independent of your mailbox. Remember to export it periodically: a closed account, a change of provider or a tool migration, and the log is gone. An external hard drive dedicated to archives and updated quarterly costs less than an hour of a lawyer's time.
The thermal paper blind spot. Roll-fed fax machines print on paper whose chemical developer degrades under light, heat and contact with plasticisers. The Archives de France have long advised against keeping thermal printouts as originals: in practice, reckon on two to five years before they fade away entirely. If your old faxes are still sitting on that medium, scan them now.
For how long? The period depends on the content, not on the fax
There is no such thing as a "fax retention period". The law is indifferent to the medium: it's the nature of the document transmitted that sets the deadline. The periods below are based on the benchmarks published by Service-Public.fr (section "Durée de conservation des documents de l'entreprise") and on the French Commercial Code.
| Nature of the faxed document | Usual retention period | Basis |
|---|---|---|
| Customer or supplier invoice | 10 years | Commercial Code, art. L123-22 |
| Commercial contract concluded electronically | 5 years (10 years if > €120) | Consumer Code |
| Payslip (employer) | 5 years | Labour Code, art. L3243-4 |
| Tax returns and supporting documents | 6 years | Book of Tax Procedures |
| Routine commercial correspondence | 5 years | General limitation period |
| Patient records in a healthcare establishment | 20 years from the last stay | Public Health Code, art. R1112-7 |
| Staff register | 5 years after the employee leaves | Labour Code |
Two common-sense rules round out the table.
The longest-period rule. When a fax contains several types of information — a purchase order together with contractual correspondence, for instance — apply the longest period to the whole.
The minimisation rule. Conversely, the GDPR prohibits keeping personal data beyond the purpose pursued. Holding on to an unsuccessful applicant's fax for ten years isn't prudence, it's a breach. The CNIL recommends defining, for each category of document, an intermediate archiving period followed by effective deletion. We expand on this point in our article on fax confidentiality and the GDPR.
Format: why PDF/A rather than plain PDF
A fax received by email generally arrives as a PDF or a TIFF. Both open fine today. The question is whether they will still open in 2040.
PDF/A (the ISO 19005 standards) is a variant of PDF designed for long-term archiving: fonts must be embedded, no external content, no JavaScript, no encryption, declared colour profile. A PDF/A is a self-contained file — it relies on no outside resource to display correctly.
Conversion is possible with most office suites, LibreOffice included, or with PDF management software. For a practice handling several dozen faxes a week, a duplex document scanner with an automatic feeder and native PDF/A output turns a half-day chore into a background task.
Naming your files: the convention that saves you
An archive you can't find is an archive you've lost. Adopt a single scheme and apply it without exception:
YYYY-MM-DD_recipient_subject_pagecount_status.pdf
2026-09-12_CPAM-Nantes_accident-certificate_3p_OK.pdf
Putting the date first guarantees natural chronological sorting in any file explorer. The status at the end lets you spot failed transmissions to resend at a glance. Avoid accents, spaces and the characters / : *, which cause trouble when migrating between systems.
Evidentiary value: what really strengthens an archived fax
A fax is not a signed original. Under French law, article 1366 of the Civil Code grants electronic writing the same evidentiary force as paper writing on two conditions: that the author can be duly identified, and that the writing is created and kept in conditions that guarantee its integrity.
The first point is shaky for a fax: nothing technically identifies the sender beyond the CSID (the declared station identifier, which anyone can configure freely). The second, however, is entirely down to you. Four measures make the difference.
Timestamping. A date held inside the file can be changed in three clicks. A qualified timestamp, issued by a trust service provider within the meaning of the European eIDAS regulation, attests that a document existed at a given moment. The list of qualified French providers is published by ANSSI.
The hash. Computing a SHA-256 fingerprint for each file and recording it in a separate log makes it possible to demonstrate, years later, that the file has not changed by a single byte.
The event log. The NF Z42-013 standard, transposed internationally as ISO 14641, sets out the requirements for an electronic archiving system with evidentiary value: traceability of access, timestamped logging, dual storage on separate media. No small business needs a full-blown archiving system, but the logic applies on a smaller scale.
Consistency. A judge gives more credit to a company that applies the same procedure to all its faxes, systematically, than to one that produces a single isolated document. Set yours out on one page and file it in a lever-arch binder alongside your quality procedures — or in a shared folder, as long as it exists.
Worth remembering: evidentiary value isn't decreed at the moment of the dispute, it's built through consistent, documented practice that predates the conflict.
Where to store: balancing accessibility and security
The 3-2-1 rule
Borrowed from backup professionals, it remains the best yardstick: 3 copies of the data, on 2 different types of media, with 1 kept off site.
For a ten-person practice, that might look like:
- the working copy on the office server or NAS;
- an automatic backup to a two-bay NAS in RAID 1, in another room;
- an encrypted copy with a hosting provider, or on a drive rotated and stored off the premises.
Encryption is not optional as soon as health data, banking data or identity documents are involved. The GDPR does not mandate it by name but cites it as an appropriate security measure in article 32.
The trap of using your mailbox as an archive
Leaving faxes sitting in your email is the most widespread practice — and the riskiest. A mailbox fills up, gets purged automatically, disappears when an employee leaves, and its contents are rarely backed up according to the 3-2-1 rule. Treat email reception as a front door, never as a place of storage. How that reception works in detail is described in our fax-to-email guide.
The paper archives that remain
Some documents must be kept in physical form. Store them flat, away from light, in a room with stable humidity, and avoid metal paper clips, which rust. Good-quality acid-free cardboard archive boxes cost a few euros and prevent accelerated yellowing.
Frequently asked questions
Does an "OK" transmission report prove receipt?
It proves that a machine answered at the number dialled and acknowledged the pages transmitted. It proves neither the identity of the recipient nor that the document was read. It's a solid piece of evidence, rarely sufficient on its own: pair it with the document and, for sensitive transmissions, back it up with registered post.
Do I need to keep the paper fax if I have the PDF?
If the PDF is the one produced by the fax gateway (i.e. the image as received), it constitutes a faithful copy. A reliable copy within the meaning of article 1379 of the Civil Code has the same evidentiary force as the paper original. Even so, keep the original for as long as a challenge remains possible, particularly for private deeds.
How long should a private practice keep a patient's faxes?
The 20-year period under article R1112-7 of the Public Health Code applies to establishments. For practitioners in private practice, no period is set by law; the Conseil national de l'Ordre des médecins recommends aligning with those 20 years, bearing in mind the limitation periods for medical liability.
Can faxes be destroyed after scanning?
Yes, provided the digital copy meets the reliability requirements of decree no. 2016-1673: identical reproduction, integrity guaranteed by a timestamp and a fingerprint, storage under controlled conditions. Otherwise, destroying the original deprives you of a means of proof.
Does the GDPR require me to delete my fax archives?
It requires you to set a retention period and stick to it. Once the statutory or contractual period has elapsed, personal data must be deleted or anonymised. A cross-cut document shredder is the bare minimum for paper; for digital media, use secure erasure on any drives taken out of service.
The essentials in ten lines
- An archived fax means three items: the document, the transmission report, the provider's trace.
- The retention period depends on the content, not the medium: 5 years for correspondence, 10 years for accounting records, up to 20 years in healthcare.
- Thermal paper is not archiving: scan it within two years at most.
- Prefer PDF/A to ordinary PDF, and use a naming convention with the date first.
- Integrity is demonstrated through qualified timestamping (eIDAS) and the SHA-256 fingerprint.
- Apply the 3-2-1 rule and encrypt anything containing sensitive data.
- Your mailbox is a front door, never a place of storage.
- The GDPR requires both a retention period and effective deletion at the end of it.
- Before a judge, a consistently applied procedure carries more weight than an isolated document.
- For high-stakes transmissions, back the fax up with registered post: the cost is trivial next to the risk.
Need to send a fax before archiving it? The sending form and the list of supported countries are two clicks away.
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