Relocating Your Business: Keeping Your Fax Number

Short answer: a fax number is not an accessory to your lease, it is a receiving address printed on your prescription pads, your terms and conditions, your supplier records, professional directories and your public-sector partners' forms. Losing it during a move means silently losing incoming documents for months, without ever knowing which ones. The good news: in France, number portability applies to geographic numbers used for fax just as it does for voice, under the conditions set by Arcep — but it has one formidable limit, the numbering zone. Three rules: start the process at least six weeks before handing over the keys, decouple the number from the physical line by switching to an online fax service before the move, and maintain an overlap period in which the old and new channels both receive in parallel.

What a move actually breaks in a fax flow

The usual reflex is to treat fax as just another line: you cancel it at the old address, order one at the new address, and see how it goes. That is a flawed line of reasoning, because fax is not an outgoing channel, it is first and foremost an incoming one.

The outgoing number is under your control. The day it changes, you inform your correspondents, you update your cover sheet, and the matter is settled within days.

The incoming number is not under your control. It lives in systems you do not own: a client's supplier record, a hospital's internal directory, a pension fund's address book, an agreement signed in 2014, a downloadable PDF form on a local authority's website. Nobody will tell you that a document was sent to a number that is now inactive. At best, the sender receives a failure report and calls back. At worst, the number has been reassigned to a third party and your document ends up with a stranger — with consequences you can easily imagine if the page contains health data, payroll details or a contractual document.

The real timeline is longer than the announced one. Installing a fixed line in new or renovated premises sometimes requires a connection, an operator visit, internal cabling. Between the contractual date and the date the equipment genuinely receives, two to three weeks often pass. Those are exactly the weeks during which you are telling your partners that "everything is working."

Portability: what you can keep, what you lose

Portability of fixed numbers is a right regulated by Arcep. In practice, for fax use, you need to understand three concepts.

The numbering zone, the real ceiling

A French geographic number is tied to an elementary numbering zone (ZNE). Portability is granted as of right when you change operator without leaving the zone. If you move from Lille to Bordeaux, your 03 number does not automatically follow: the numbering plan links the area code to a geographic area. In concrete terms:

The last row is the lesson of the table. A fax number hosted on an online service is independent of the postal address: it lands in a mailbox, not on a wall socket. This is the only configuration in which a move literally poses no problem.

The RIO, to be requested before cancelling

The operator identity statement (RIO) for the line concerned is obtained from your current operator. Absolute rule: never cancel before the porting process has been initiated. Cancelling first releases the number, which goes back into the reassignment pool — at which point it becomes unrecoverable. This is the number one mistake in business relocations, and it is irreversible.

The end of the PSTN changes the picture

The legacy switched telephone network is being shut down area by area, and analogue lines are disappearing from new offers. One practical consequence: in recent premises, there is no longer a usable analogue socket for a conventional fax machine, and fax transmission over VoIP remains fragile (compression, packet loss, T.30 protocol desynchronisation). If this concerns you, the topic is covered in detail in our article on the end of the PSTN and analogue fax lines. A move is precisely the right moment not to plug a doomed piece of hardware back in.

The timeline in six milestones

D‑60: inventory of publication points

Before any technical step, list where your number is written. The exercise seems trivial; it never is. Review:

• letterhead, cover sheets, business cards, ink stamps;
• quotes, invoices, terms of sale, framework contracts in force;
• supplier records held by your clients (request the update in writing);
• professional directories, professional bodies, federations, chambers of commerce;
• PDF forms hosted by third parties (the most stubborn of all);
• email signatures, website, online business listing;
• device manuals, labels stuck on the machines themselves.

A simple relocation tracking notebook kept by hand, with a column for "publication point / owner / update date / confirmed", beats a shared spreadsheet that nobody opens. Tick it off with a pen — that is what actually gets done.

D‑45: choosing the architecture

Only two scenarios are worth considering.

Scenario A — the physical line is carried over. You order another line, a fax machine, consumables. You keep the team's habits. You also keep the breakdowns, the dependency on the premises, and the certainty of replaying the same problem at the next move.

Scenario B — the number is ported to an online fax service. The historical number is transferred to a digital fax provider; incoming faxes arrive as PDFs in a dedicated mailbox, outgoing ones are sent from any workstation. The address of the premises becomes irrelevant. This is the recommended scenario in 90% of cases, and it is precisely the principle behind the virtual fax number.

Scenario B has a hidden cost that needs naming: you must appoint a mailbox owner. Fax reception landing in a shared mailbox with no owner is fax reception that ends up ignored.

D‑30: launch the porting and open the overlap

Submit the portability request with the RIO. In the same move, open the new channel without closing the old one. For six to eight weeks, both must be able to receive. This is the only way to measure residual traffic: if the old number is still receiving three documents a week at D+30, your publication inventory is incomplete, and you know you need to keep looking.

D‑15: the notification campaign

Send a structured letter or email to your regular correspondents. The message should contain four pieces of information and nothing else: the old number, the new one (or confirmation that the number is unchanged), the switchover date, and the date the old channel will be shut down. For critical partners — a hospital department, an accountancy firm, a public-sector client — back this up with a confirmation call and note the date in your notebook.

D‑7: securing outgoing archives

A move is exactly when paper transmission reports vanish. Yet those are your proof of sending. Two useful actions:

• gather the transmission logs stored in the fax machine (most devices keep several hundred and can print them out before disconnection);
• digitise the binders of reports still relevant given your limitation periods. An automatic document feeder scanner swallows an entire binder in half an hour, where an office multifunction device would take you all afternoon.

On the conditions to be met for destroying paper originals after scanning, the rule is precise and worth reading: see reliable copy and destruction of the original.

D+30: the residual traffic audit

One month after the switchover, record what is still arriving on the old channel. Trace each sender back to its publication source and correct it. It is two hours of thankless work that prevents a compliance incident six months later.

The awkward question: what happens to the abandoned number

If you do not port the number and simply let it go, it is returned to the operator and then, after a quarantine period, reassigned. The new holder will receive your documents. This is not theoretical: it is the classic mechanism of data leakage through directory obsolescence, and the CNIL regularly points out that the data controller must take measures to prevent disclosure to unauthorised recipients. A medical practice, an HR department or a law firm that abandons a number without purging its publication points exposes data to an unknown third party.

Three risk-reduction measures:

1. Port the number rather than abandon it, even if you no longer intend to use it: keeping it for a few euros a month on an online service, until the traffic dies down, costs less than an incident.
2. Route the old number to a monitored collection mailbox, with an automatic reply sent to the sender.
3. Document the closure in writing in your register, with the date, the reason and the notifications sent.

If a sensitive document slips through despite everything, the course of action is described in our article on the fax sent to the wrong number.

Temporary premises and multi-site setups

Many relocations go through an interim phase: shared offices, a coworking space, activity split between home and a site under renovation. In this configuration, a physical line is structurally impossible — a coworking space will not allocate you a dedicated analogue socket, and house rules generally prohibit installing a noisy device in an open-plan area.

It is also the period when confidentiality degrades the most: documents printed on a shared copier, pages forgotten in the output tray, a screen visible from the corridor. Two modest accessories solve most of the problem: a privacy screen filter on the workstations used to view incoming faxes, and a cross-cut shredder right next to the desk, so that a sensitive page never ends up in a communal bin. For a home workstation, the full set of best practices is detailed in our guide to faxing while working from home.

Frequently asked questions

Can you keep a fax number when moving to another region?

Not while keeping a conventional geographic line: the area code stays tied to its zone. However, a number ported to a digital fax provider can be kept regardless of the company's address, since reception no longer has a physical endpoint. It is the only reliable route for an inter-regional move.

How long does fixed-number portability take?

The actual port usually takes place within a few working days once the request has been validated, but the preparation (obtaining the RIO, checking eligibility, coordination between operators) lengthens the overall process. Allow four to six weeks end to end, and never announce a switchover date to your partners before written confirmation from the receiving operator.

Do you need to notify clients of a number change by registered post?

Not for simple information purposes. Registered post is justified when the number appears in a current contract that designates fax as a valid means of notification: the change must then be notified in the form set out in the contract, failing which an adverse notification sent to the old number could be deemed valid.

What about faxes received during an outage?

Nothing can be recovered: a fax that is not received is not stored anywhere. That is precisely why the overlap period is non-negotiable. If an outage did occur, identify the exact window and ask your critical correspondents to resend, keeping a written record of the request.

Can an old fax machine be reinstalled in new premises?

Technically sometimes, practically rarely. Without an analogue socket, you need a VoIP adapter, and the reliability of the fax protocol over IP remains poor. If you are set on keeping a device, go for a compatible laser multifunction printer with a fax module, and test it before dismantling the old one. But a move is the right moment to raise the question of migration: our 6-step migration plan covers this point.

In summary

• A fax number is a receiving address published everywhere: losing it causes silent document losses that are never reported.
• Never cancel before the porting process has been initiated: a released number is lost for good and may be reassigned to a third party.
• Geographic portability runs up against the numbering zone; only a number hosted on an online fax service survives an inter-regional move.
• Plan for six to eight weeks of overlap with both channels active, then audit residual traffic at D+30.
• Draw up the inventory of the number's publication points before any technical step: that is where 80% of the outcome is decided.
• A number abandoned without purging directories is a risk of disclosing data to an unauthorised recipient.
• Use the move as an opportunity to decouple fax from your premises: see the list of available countries and the FAQ before deciding.