Multi-site fax: organising fax numbers across a branch network

Short answer: in a multi-site organisation, the fax problem is almost never the machine — it is the numbering plan and the routing. The set-up that lasts rests on three decisions: keep one number per site (partners have had it on file for years), have every inbound flow land in named functional mailboxes rather than an individual's inbox, and maintain a mapping table of number → site → mailbox → owner, updated at every relocation. A single national number looks appealing on paper; in practice it creates a bottleneck at head office and destroys traceability by establishment.

About MondialFax. This article is a practical guide, independent of any carrier or vendor. MondialFax sends faxes free of charge and without registration to seven destinations (France, Belgium, Germany, Spain, Italy, Portugal, Canada). It does not assign numbers and does not handle reception: the receiving scenarios described here assume a third-party provider. See receiving a fax and our fax-to-email guide.

There is a precise moment when faxing stops being a housekeeping detail: the moment you open the company's spreadsheet of telephone lines. Thirty-two locations, forty-one fax numbers listed, eleven of which nobody can say whether they still ring. Three branches have a physical fax machine plugged into a router, two use a cloud provider signed up for locally on the branch manager's credit card, and head office receives faxes by email addressed to a site that closed in 2023.

This mess is not negligence. It is the mechanical product of twenty years of openings, acquisitions and relocations, accelerated by the gradual shutdown of the legacy copper network and Orange's withdrawal of PSTN access from sale. Each site improvised its own solution, on its own, at the moment its analogue line went down.

The good news: restoring order costs less than you would think, provided you treat the subject as a numbering plan, not an equipment purchase.

Why a branch network has a fax problem all of its own

A standalone practice settles the matter in an afternoon: it subscribes to a fax-to-email service, keeps its number and forgets about it. A multi-site organisation faces four difficulties that simply do not exist at a single establishment.

Contractual fragmentation. The lines were taken out on different dates, with different carriers, sometimes in the branch's name rather than the parent company's. When the time comes to port a number, the carrier demands proof in the exact name of the account holder — and that account holder is a limited company absorbed in 2019.

Asymmetric usage. In a network of twenty branches, three receive 80% of the faxes (those handling claims, financing files or laboratory orders) and seventeen receive two a quarter. Applying the same solution everywhere means either overpaying or under-provisioning.

Responsibility for handling. A fax received at head office on behalf of a branch has to be forwarded on. Every hand-off is a delay, and in some trades — insurance loss adjusting, transport, healthcare — the delay is the value of the document.

Compliance. The GDPR draws no distinction between a paper fax left forgotten in a tray and a fax PDF landing in the personal inbox of an employee away on leave. We set out the obligations in our guide to fax confidentiality and the GDPR.

Step 1: map before you decide

No architectural decision holds up without an inventory. The table can be built in a week, by working through carrier invoices and questioning site managers.

It is the last column that most often takes people by surprise. A fax number printed for twelve years on prescription pads, purchase orders or terms and conditions survives for a very long time in partners' systems. A health insurer, a laboratory or a freight forwarder will not update its database just because you sent an email. The number will keep receiving documents for years.

In practical terms: dig out the archives, including the paper files. A portable label printer used to physically mark every wall socket and every device with its actual number saves hours of reverse engineering at cut-over.

Step 2: single number or one number per site?

This is the central debate, and the default answer leans clearly one way.

The mirage of a single national number

The argument is seductive: one number across all communications, one contract, one point of reception, internal routing by cover sheet or keyword. In practice, three snags:

• Sorting becomes a human task. Incoming documents arrive with no reliable metadata. Automatic routing by text recognition works on standardised forms, not on a handwritten page scanned at an angle. Someone, somewhere, opens every PDF to decide where it goes.
• You lose proof of establishment. In a dispute, knowing that a document arrived on the Nantes branch number at 2:12 pm is worth more than knowing it arrived at head office and was then forwarded on an uncertain date.
• You do not switch off the old numbers anyway. They keep receiving. So they still have to be maintained, which wipes out the promised saving.

The set-up that holds: one number per site, centrally administered

The sensible compromise is to decouple the number from the contract. Each site keeps its historic number as a DDI, but all the numbers are grouped under a single contract, administered by IT or facilities, with routing defined centrally.

In concrete terms, that means:

1. Obtaining the porting mandate for every live number, together with the line's RIO code while it is still active.
2. Consolidating the numbers with a single cloud fax provider or onto the company's SIP trunk.
3. Linking each number to a functional mailbox (fax.nantes@…) rather than to a person.
4. Leaving dormant numbers active for twelve months, redirected to a monitoring mailbox, before termination.

That last point is the most neglected. Cutting a number off on cut-over day means discovering six weeks later that a client had been sending its orders there since 2011 and has stopped ordering without a word.

Step 3: routing, where it all plays out

A properly ported number that dumps its PDFs into a mailbox nobody checks is no better than an unplugged fax machine.

Functional mailboxes, never personal ones

The rule is simple and admits no exception: the receiving address is tied to a function, not to an individual. fax.claims@, fax.orders@, fax.reception-lyon@. A person leaves, the function remains. That solves absence, turnover and departures in one stroke — and it simplifies the access-rights management required by the GDPR, since you can prove who had access to what by looking at the group's members.

Acknowledgement of handling, not just of receipt

The sender's transmission report proves the document went out. It proves nothing about what became of it at your end. In trades where a fax carries a deadline, define a collection rule: the mailbox is checked twice each working day, every document is time-stamped on opening and filed in the client record. A duplex desktop scanner remains useful in branches that still receive paper through other channels and want to feed the same digital file.

Plan the fallback route

Every centralised architecture has a point of failure. If the branch's internet link goes down, outbound sending stops. Two inexpensive safeguards:

• A 4G backup router shared across the site's critical uses, taking over for the duration of the outage.
• A written fallback sending procedure: the document is passed to the neighbouring site or to head office, which sends it and returns the report. That does of course require an up-to-date list of numbers — hence the value of the mapping exercise in step 1.

Step 4: sizing without overpaying

The real cost of business faxing splits between the per-number subscription, page volume and human time. It is the third item that dominates by far, and it is the only one nobody measures.

On ATA set-ups, transmission failures almost always come down to transcoding. We covered T.38 settings and the alternatives in fax over VoIP: why T.38 fails. A well-known-brand analogue telephone adapter (ATA), correctly configured for G.711 with silence suppression off, rescues more transmissions than switching provider.

Step 5: document it, or none of it holds

A multi-site architecture degrades within eighteen months if it is not written down. The minimum deliverable runs to three pages:

• The mapping table of number → site → mailbox → owner, dated and version-controlled.
• The site-opening procedure: which number is ordered, on which contract, linked to which mailbox, who updates the table.
• The site-closure procedure: redirection of the number to the monitoring mailbox, how long it is maintained, termination date, notification of known partners.

This document lives in the same place as the telephone numbering plan. Keeping it separate guarantees it will be forgotten. A networked multifunction printer with a scan-to-email function is a useful replacement for the fax machine at low-volume sites — provided it is entered in the same table, otherwise it becomes one more blind spot.

A timetable you should not simply endure

The shutdown of Orange's copper network is taking place in waves of municipalities, following a schedule published batch by batch and overseen by Arcep. The dates have shifted — the delay announced in early 2026 for some households was a reminder of that — but the trajectory does not change: the analogue lines still carrying fax machines will disappear.

For a branch network, that means the deadlines do not fall at the same time from one location to another. A branch in an already-closed area has to switch now; another may have three years ahead of it. Managing site by site, using the lists of municipalities published by the operator, avoids both panic and paralysis.

The pragmatic rule: do not wait for the closure notice before acting on sites with high inbound fax volumes, and deal with zero-volume sites by simply abandoning the number, with the decision documented.

Frequently asked questions

Can a fax number be kept when a branch moves to another département?

Yes, in most cases, as long as the number is hosted on a cloud fax service or a SIP trunk: it is no longer tied to a physical local loop. That is precisely the point of decoupling number from address. Geographic numbering constraints apply to allocation, not to retention.

Does a branch need a fax number separate from its telephone number?

Yes. Sharing the same line requires automatic switching between voice and data, which fails regularly on IP infrastructure, and makes a dedicated receiving mailbox impossible. A dedicated number costs a few euros a month and eliminates an entire category of faults.

How long should a fax number be kept after a site closes?

Twelve months is a reasonable minimum, with redirection to a monitored mailbox. Institutional partners and trade databases update slowly. Extending to twenty-four months for regulated activities remains cheap relative to the risk.

How should inbound faxes be handled while a branch is closed for holidays?

By temporarily redirecting the functional mailbox to a duty mailbox, never by forwarding to a personal address. The redirection is documented, dated, and automatically reverts on the planned date.

Does an occasional overseas send justify a subscription?

No. For an occasional need, a registration-free sending service is enough. See our destination pages and the guide to sending a fax abroad.

In summary

• A multi-site network's problem is not the hardware but the numbering plan and the routing.
• Start with a map: number, site, contractual account holder, platform, actual volume, recipient, external circulation.
• Prefer one number per site administered under a single contract over a single national number, which centralises human sorting and destroys traceability.
• Route to functional mailboxes, never to personal addresses.
• Maintain the numbers of closed sites for at least twelve months with monitored redirection.
• Write down the site-opening and site-closure procedures, and keep the mapping table up to date.
• Manage the end of copper site by site, according to the closure schedule applicable to each municipality.