Customer list taken by a former employee who joined a competitor: what can you do?

October 27, 2026  | William MAK

A sales executive resigns, joins a competitor, and it turns out he emailed himself the customer list before leaving. What can be done, against whom, and when? And what does the hiring company risk?

In brief

• Forwarding a customer file to a personal email account breaches the duty of loyalty, but does not always justify dismissal for gross misconduct or an award of damages.
• What the law sanctions is the use of the file to divert customers: that is what must be proved.
• The key tool is an application under Article 145 of the French Code of Civil Procedure, which makes it possible to have the use of the file established, by surprise, at the competitor’s premises.
• The action targets the new employer first: it is more solvent than the former employee and the real beneficiary of the file.
• Time works against the victim: digital data disappears quickly.

An all too familiar scenario

It is a situation we see often: the key account manager resigns to embark on “a new adventure”. A few days later, the IT department discovers that one Sunday evening he sent himself, from his work email to his personal address, an export of his territory from the CRM: customer names, contacts, direct phone numbers, quotation history and pricing terms. Three weeks after he leaves, two long-standing customers report having been approached by a direct competitor.

The managing director then has three questions: can the company take action, against whom, and above all, how can it prove what it suspects?

Is a customer list legally protected?

Yes, but that protection rests on several legal grounds. No statute gives a company a property right over its customers, who remain free to choose their suppliers. The file that brings this information together, however, has a value of its own and enjoys several forms of protection, which may apply cumulatively.

Under criminal law, the criminal chamber of the Cour de cassation holds that customer information is property capable of being the subject of criminal breach of trust (abus de confiance). It upheld that offence against an employee who had used information received in the course of her duties “by unfair means with the aim of attracting part of that clientele to another company” (Cass. crim., 22 March 2017, no. 15-85.929). The offence carries five years’ imprisonment and a fine of 375,000 euros (Article 314-1 of the French Criminal Code).

Under civil law, the file may be protected as a trade secret (Articles L. 151-1 et seq. of the French Commercial Code), subject to an often overlooked condition: the company must be able to show “reasonable protective measures” taken to keep it confidential. A confidentiality clause, an IT policy, restricted access rights or a “confidential” label on the files may then prove decisive. Failing that, the company will have to rely on the general law of unfair competition (Article 1240 of the French Civil Code).

What can the former employee be held liable for?

While the contract is in force, the employee owes a duty of loyalty (Article L. 1222-1 of the French Labour Code). He may take company documents only if they are strictly necessary for the exercise of his rights of defence in a dispute with his employer, and the burden of proving this lies on him (Cass. soc., 9 November 2022, no. 21-18.577). A complete customer file rarely passes this test.

A word of caution, however: a mere transfer is not necessarily enough to establish misconduct justifying dismissal. The Cour de cassation upheld a court of appeal that had found the dismissal of an employee who had forwarded an email containing confidential data to her personal account to be without real and serious cause. The judges had taken into account, in particular, the lack of evidence of any disclosure to third parties, her length of service and the absence of any previous warning (Cass. soc., 9 April 2025, no. 24-12.055). Conversely, repeatedly sending the company’s address book to competing companies helped, together with other complaints, to establish the gross misconduct found by the court of appeal, which the Cour de cassation did not overturn (Cass. soc., 15 December 2010, no. 08-42.486). The volume of data, its sensitivity and above all its destination are therefore decisive.

When it comes to compensation, the scope is narrow. An employee’s financial liability towards the employer requires serious misconduct with intent to harm (faute lourde) (Cass. soc., 25 January 2017, no. 14-26.071), which implies “the employee’s intention to harm the employer in committing the wrongful act” (Cass. soc., 22 October 2015, no. 14-11.291). Seeking to serve one’s own interests is not enough. Moreover, a former employee is rarely in a position to pay a substantial award.

Once the employment contract has ended, freedom remains the rule: the former employee may join a competitor and even approach his former employer’s customers. In principle, that freedom can only be restricted by a valid non-compete clause, that is, one that is essential to protect the company’s legitimate interests, limited in time and space, tailored to the specific features of the job and subject to financial consideration (Cass. soc., 10 July 2002, no. 00-45.135). Using a misappropriated customer file, on the other hand, remains wrongful whether or not there is such a clause.

What does the hiring company risk?

Hiring a competitor’s employee is not wrongful in itself: competition is free and talent moves. The new employer does, however, incur liability when it knowingly exploits the information its recruit has brought along.

Three legal grounds may then apply cumulatively. First, unfair competition, from which, as the commercial chamber of the Cour de cassation reiterates, “damage, even if only moral, is necessarily inferred” (Cass. com., 12 February 2020, no. 17-31.614), although the victim must still show its extent. Second, trade secrets, whose use is unlawful where the company “knew, or ought to have known in the circumstances” that the information had been obtained unlawfully (Article L. 151-6 of the French Commercial Code). Finally, under criminal law, handling the proceeds of an offence (recel), which carries five years’ imprisonment and a fine of 375,000 euros (Article 321-1 of the French Criminal Code).

The risk is even clearer when the recruit is bound by a non-compete clause. In a case where the new employer’s appeal was dismissed, the employer, although informed of the clause and served with formal notice, had kept the employee in post: the commercial court’s interim relief judge ordered it to prohibit the employee from any activity within it that put him in direct competition with his former employer, subject to a penalty of 400 euros per day for three months. The court of appeal held that the employee’s statement in his new contract that he was free of any commitment was of no effect, since the new employer had been informed of the clause. The Cour de cassation, for its part, upheld the interim relief judge’s decision not to wait for the ruling of the employment tribunal hearing the validity of the clause, since interim relief is only provisional (Cass. com., 9 June 2021, no. 19-14.485).

For the hiring company, a few precautions help to limit this risk. It is wise to ask the candidate to confirm in writing that he is bringing no files or documents from his former employer, to check before hiring whether he is bound by a non-compete clause, and to prohibit any import of data when he arrives. If the former employer serves formal notice, the company must respond without delay and keep a record of the steps it has taken.

How can the use of the file at the competitor be proved?

This is the heart of the case. The transfer of the file can be proved internally; its use, however, takes place at the competitor. Suing directly would expose the company to having its claims dismissed for lack of evidence, while alerting the other side.

Article 145 of the French Code of Civil Procedure makes it possible, “if there is a legitimate reason to preserve or establish, before any trial, evidence of facts on which the outcome of a dispute may depend”, to obtain an investigative measure. When it is sought by ex parte application, without the competitor being informed, this measure allows a commissaire de justice (judicial officer), assisted by an IT expert, to search the competitor’s premises and IT systems for the transferred files and any documents derived from them. In practice, it is a surprise visit, authorised and supervised by the judge.

The effectiveness of the measure depends on the quality of the application, and the case law does not forgive approximation. The measures must be “limited in time and in scope and proportionate to the objective pursued” (Cass. 2e civ., 25 March 2021, no. 20-14.309). Overly generic keywords (“Google”, “Linkedin”, “employee”) thus led to the quashing of a judgment that had refused to set aside the order (Cass. 2e civ., 10 June 2021, no. 20-11.987). The search must be targeted: file names, customer codes and names, a defined period.

The application must also explain precisely why the competitor should not be forewarned. In a published judgment of 16 April 2026, the Cour de cassation quashed a court of appeal decision that had set aside an order, whereas the application set out detailed evidence giving grounds to fear that evidence would be concealed and justifying the element of surprise, and whereas a copy of the application and of the order had indeed been handed over before the measure was carried out (Cass. 2e civ., 16 April 2026, no. 23-12.123). The same judgment specifies that, where the order authorises access to the personal computer or email of an employee of the company being searched, in that case the applicants’ former employee, a copy of the application and of the order must also be handed to him.

The competitor’s trade secrets do not stand in the way of the measure, provided it is necessary and proportionate (Cass. 2e civ., 10 June 2021, cited above), and the judge may place the seized documents in provisional escrow (Article R. 153-1 of the French Commercial Code). Above all, for Article 145 orders made on or after 1 October 2026, Decree no. 2026-683 of 27 July 2026 imposes strict time limits: unless the judge sets a different period, the order must be enforced within three months of its date, failing which it lapses, as the court must note of its own motion (Article 495 of the French Code of Civil Procedure); where the order has been served, any application to set it aside must be made within one month of service, failing which it is inadmissible (Article 496). The timetable is therefore tight, for the victim and the targeted competitor alike.

The action plan

1. Preserve internal evidence. Avoid reassigning or deleting the former employee’s mailbox and computer, keep the connection logs and have the transfers recorded by a commissaire de justice. Emails from the work mailbox are presumed to be work-related and may be consulted in the employee’s absence, unless they are identified as personal (Cass. soc., 15 December 2010, cited above).
2. Identify precisely what has gone: which files, what volume, what data, on what date and to which address.
3. Review the employment contract, the IT policy and any non-compete clause, checking in particular whether the clause is valid and how long the company has to waive it.
4. Set up commercial monitoring by asking teams to report any approach to customers and to keep anything that can prove it (emails, offers, witness statements).
5. Bring an Article 145 application to gather evidence.
6. On the basis of the evidence gathered, bring proceedings for unfair competition or trade secret infringement to obtain an injunction against use of the file, its handover or its destruction subject to a penalty (Article L. 152-3 of the French Commercial Code), together with damages and, where appropriate, publication of the decision.

Frequently asked questions

Is forwarding a customer file to a personal mailbox gross misconduct?

Not automatically: it all depends on the volume and sensitivity of the data, whether it was passed on to third parties and the employee’s record (see above). If the employee is still on the payroll, disciplinary proceedings must be initiated within two months of the facts coming to light (Article L. 1332-4 of the French Labour Code).

Can a former employee approach his former customers?

Yes, in principle, unless he is bound by a valid non-compete clause. He is, however, prohibited from using a misappropriated customer file, disparaging his former employer or disrupting its business.

Which court has jurisdiction?

The employment tribunal (conseil de prud’hommes) for claims against the employee under the employment contract; the commercial court, or the economic activities court (tribunal des activités économiques) where it is being piloted, for disputes between two commercial companies. The ex parte application is filed, at the applicant’s choice, with the court that would hear the merits or with the court of the place where the measure is to be carried out (Article 145, paragraph 2, of the French Code of Civil Procedure).

What are the time limits for taking action?

The limitation period is two years for a claim relating to the performance of the employment contract (Article L. 1471-1 of the French Labour Code) and five years for an unfair competition claim (Article 2224 of the French Civil Code). In practice, though, the urgency is far more immediate: a few weeks may be enough for a file to be reworked, merged with other data or deleted.

Can unfairly obtained evidence be used?

Since the full court judgment of 22 December 2023, unlawful or unfairly obtained evidence is no longer automatically excluded: the judge weighs the right to evidence against the competing rights, and the evidence must be indispensable and the infringement strictly proportionate to the aim pursued (Cass. ass. plén., 22 December 2023, no. 20-20.648). This is no blank cheque: evidence gathered under the court’s supervision remains far safer.

Conclusion

Faced with the theft of a customer file, the first reflex is often to send the former employee a particularly firm registered letter. This is generally the wrong strategy: it warns the other side without, on its own, gathering any evidence at all.

The winning strategy is the reverse: preserve your evidence, target the real beneficiary of the file, gather proof of its use by surprise, then negotiate or litigate from a position of strength.

MOSAIK advises companies at every stage of these matters: employment law, Article 145 applications, unfair competition, trade secrets and commercial litigation.

William Mak

Lawyer - Founder