Spain’s Law 10/2025 on customer service sets, for the first time, mandatory maximum deadlines for handling complaints: 15 working days as a general rule and just 5 working days when the dispute involves an improper charge. Those deadlines only start running if there is reliable proof of when the complaint was sent and what it contained.
Without that proof, the company can dispute the date of receipt, claim the message arrived without the content you submitted, or deny receiving it altogether. The legal deadline becomes unenforceable.
What Law 10/2025 requires from customer service departments
Law 10/2025, published in Spain’s Official State Gazette (BOE) in 2025, sets minimum quality standards for customer service operations across two groups:
- Providers of essential services: water, gas, electricity, telecommunications and financial services companies.
- Large companies with more than 250 employees or more than €50 million in annual turnover, regardless of sector.
Key obligations:
- Maximum resolution deadline of 15 working days for any general complaint, counted from the moment the company receives it.
- Reduced deadline of 5 working days for complaints about improper charges or billing errors.
- Multichannel access: phone, email and, in many cases, a web form.
- Prohibition of routing customers exclusively to automated systems when a human agent is requested.
Non-compliance may trigger administrative sanctions and, where the customer has suffered a financial loss, civil liability.
Why the dispatch date is the critical variable
The deadlines in Law 10/2025 are calculated from the moment the company receives the complaint, not from when the customer writes it or attempts to send it. This creates a single critical point: if there is no certified record of the moment and the content of the submission, the company can:
- Claim the complaint arrived several days after the actual date.
- Argue that the document reached them without the content you describe.
- Ignore the complaint entirely and deny ever receiving it.
A standard Gmail message, an unacknowledged web form or a phone call with no recording do not constitute sufficient evidence before a regulator or a court. The burden of proof rests with the claimant: you must demonstrate that you sent it, what you sent and when.
4 options for certifying the dispatch of a complaint
1. Certified email with timestamp
Certified email is the fastest way to establish legal proof of a complaint sent electronically. Unlike a standard email, it generates a certificate that includes:
- The sender and recipient addresses.
- The full text of the message and any attachments.
- A probative timestamp (exact date and time of dispatch).
- Delivery evidence at the recipient’s server.
This certificate is accepted as documentary evidence in administrative and judicial proceedings in Spain.
2. Buromail (certified digital notification)
Buromail is the digital equivalent of the Spanish burofax, without the need to visit a post office. It certifies the dispatch, the full content of any attached document and the delivery, entirely online and within minutes.
It is particularly useful when the complaint includes supporting documentation — invoices, contracts, screenshots of charges — that must be incorporated into the certified proof.
3. Certified SMS as a complaint acknowledgement
Where a company has provided a phone number as its complaints channel, a certified SMS allows you to submit the complaint with certified proof of content, date and destination number. It generates a certificate equivalent to that of a certified email.
4. Postal burofax from Correos
The physical burofax remains legally valid, but it involves higher costs, requires a visit to a post office and delivery times can eat into the response window the law gives the company. For urgent cases such as the five-working-day deadline for improper charges, the digital route is significantly more efficient.
What the complaint must contain to have legal effect
The content of the complaint is as important as the channel through which it is sent. An effective complaint should include:
- Claimant identification: full name, national ID number (DNI/NIE) and contact details.
- Customer or contract reference number with the company.
- A clear, chronological description of the problem: what happened, when and what loss or harm resulted.
- A specific request: refund of an amount, correction of an invoice, fulfilment of a contractual obligation.
- Supporting documents: invoices, bank statements, prior correspondence, photographs where applicable.
- Reference to Law 10/2025 when invoking a specific deadline: this puts the company on notice that you know your rights and the legal time limit for their response.
Adding a digital signature to the document provides an extra layer of authenticity, particularly if the complaint may eventually proceed to court.
Companies bound by Law 10/2025
The law applies to a wide range of operators. In practice, users of the following services can demand compliance:
| Sector | Key obligation |
|---|---|
| Telephone and internet | 15 working days to resolve; human channel available |
| Electricity and gas supply | 15 days; 5 days for improper charges |
| Banking and insurance | 15 days; 5 days for billing errors |
| Water and sanitation | 15 days; in-person or remote contact |
| Large retailers (250+ employees) | 15 days; multichannel mandatory |
If the company does not respond within the deadline, you can refer the matter to the Spanish Consumer Agency (AECOSAN), to the relevant sectoral regulator (CNMC for telecoms and energy, Banco de España for financial services) or to the commercial court.
Step-by-step: how to complain with certified legal proof
Step 1. Draft the complaint
Write the complaint with all the elements listed above. Save a copy of the document before sending.
Step 2. Choose the certified channel
Use certified email or buromail if the company has an official email address for complaints. Use certified SMS if the designated channel is phone-based. Avoid web forms that do not issue a certified acknowledgement.
Step 3. Send and save the certificate
Keep the dispatch certificate generated by the platform. This document, with its timestamp and content hash, is the evidence you need if the company fails to meet its deadline.
Step 4. Note the deadline
With the certified dispatch date in hand, calculate the deadline: 15 working days (excluding Saturdays, Sundays and national public holidays) or 5 working days for improper charges. If the company does not respond in time, you already have a complete case file to escalate the complaint.
Frequently asked questions
Does Law 10/2025 apply to every company in Spain?
No. It applies to providers of essential services (electricity, gas, water, telecoms, financial services) regardless of size, and to large companies in any sector with more than 250 employees or more than €50 million in annual turnover. Small and medium enterprises outside these categories are not directly obliged, though many adopt the standards voluntarily.
Is a standard Gmail email enough to prove I sent a complaint?
Not reliably. A standard email does not certify its content or the exact time of delivery at the recipient’s server. The company may argue the message arrived on a different date or with different content. A certified email with a timestamp and content certificate provides the probative value needed.
What happens if the company responds after the 15-day deadline?
Missing the deadline is an administrative infringement. You can submit a complaint to the competent consumer authority (regional or national) or to the sectoral regulator, attaching the dispatch certificate as evidence that the deadline has passed. In some cases, the delay may give rise to compensation for losses caused.
Does buromail carry the same legal weight as a postal burofax?
Yes, provided the service provider is authorised as a trust service provider or operates as a trusted third party with qualified timestamping. Legalpin’s buromail generates a certificate with the same evidentiary guarantees as a postal burofax, with the added benefits of immediacy and no need to leave your desk.
Can I use certified email to dispute an improper bank charge?
Yes. Financial services are within the scope of Law 10/2025. You can send the complaint by certified email to the bank’s official complaints address. The dispatch certificate sets the date from which the five-working-day response deadline runs.
What if the company only accepts its web form and issues no certified acknowledgement?
Complete the form, but take a full, dated screenshot of everything you submitted. If the form does not issue a certified receipt, complement the submission with a certified SMS to the customer service number or a postal burofax to the company’s registered address. Using both channels strengthens your evidence file considerably.
General information only; does not constitute individual legal advice.
