Quick overview
- Self-employed persons, companies and associations must have a data box.
- An unread message is considered delivered after 10 days.
- You often have to file documents electronically with the tax authorities.
- You can access it via the My mailbox portal.
- The notification e-mail is not legally binding – the delivery to the mailbox is decisive.
Not sure if you have been served correctly or if the time limit for appeal has expired? We will look into your case and advise you on how to proceed.
In May 2026, there were more than 4.2 million active data boxes in the Czech Republic . Since their introduction in 2009, their number has been growing slowly, but a significant breakthrough came at the beginning of 2023 – mainly due to the legal obligation to set them up for all individuals doing business. Within a few months, there was an increase of more than one million new users.
It is important to remember that one number does not mean one person. Many people have multiple mailboxes – for example, one as a self-employed person and another as an individual. The covid pandemic has also played a role, accelerating the digitalisation of public administration and boosting trust in government online systems. In the case of individuals, the numbers are often increased by the fact that one person sets up a data box as a sole trader, often followed by another, personal box, through which, for example, property tax on housing and other private matters can be dealt with.
Tip for article
Tip: The obligation to own and use a data box applies to all sole traders. However, it is not only for them. In many ways, you will appreciate it even if you are not a sole trader. In our next article, we will advise you on how to set up a data box.
Who is obliged to have a data box?
Who must have a data box?
The obligation to have a data box currently applies to:
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All legal entities registered in the public register (e.g. limited liability companies, foundations, associations, associations of associations, institutes),
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Natural persons doing business (sole traders, persons registered in the trade register or other register),
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Public authorities (authorities, schools, medical institutions, etc.).
These persons are legally obliged to receive documents via their data box. Therefore, authorities and courts send their documents exclusively electronically via the data box portal.
However, the obligation to communicate electronically in the other direction does not yet apply as a rule. Until now, submissions can be sent to the authorities in any way.
The tax administration has stricter rules
The tax authorities insist on exclusive electronic submission for all persons for whom a data box has been established by law. This means that, for example, a sole trader cannot file a tax return on paper, otherwise he or she will receive a correction notice. If he fails to respond, a fine may follow.
In practice, we see situations where a businessman files a paper tax return even though he has a data box set up by law. The tax office then calls for corrective action and may impose a fine if the taxpayer fails to act. If you are unsure of the correct procedure to follow with the tax office, we can advise you.
How does data box delivery work?
Every message delivered is available to the user immediately after logging into their mailbox. Usually there is an email notification that a new message has been delivered, but this notification is not legally decisive – it is the status of the mailbox that matters, not the email.
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If you do not follow the instructions to send documents electronically, you will first receive a notice to correct the defect in your submission. This year an increased number of such filing defects have been noted. If you do not comply with the notice either, a fine may follow.
What about the fiction of delivery?
In general, a document that arrives in the data box of a legal or natural person is deemed to have been delivered at the moment the person logs in to the data box. However, if this does not happen within the next ten days, the so-called fiction of delivery occurs.
It is valid that after the message has been delivered to the data box, the natural or legal person has ten days to read it.
Thereafter, a legal fiction is created that the person has read the document, even if he or she has not logged into the data box at all. This has a major impact, for example, on the running of the various time limits for making representations, appeals, etc.
For example, we dealt with a case of a businessman who did not open his data box for two weeks during his holiday. In the meantime, the tax office served him with a notice to complete his submission. As the deadline had passed in the meantime, he was threatened with a penalty. However, thanks to a quick response, the situation was resolved without significant consequences.
In practice, we also encounter other cases where an entrepreneur does not open his data box for several weeks and only subsequently discovers that proceedings have been initiated against him or that he has been ordered to pay a fine. A common mistake is relying on e-mail notifications, which may not arrive at all.
However, this principle can also apply in some forms in the opposite way, i.e. when communicating with the authorities. For example, there is a recorded case of a techno party whose participants literally devastated municipal land and disturbed the surrounding area with their noise for several days. However, it cannot be said that this was an unauthorised event. In fact, the organisers duly submitted the application via the data box and, when no one replied, they took the opportunity to consider the application approved.
As of 1 January 2023, the rule on the delivery fiction has been modified in that if the tenth day of delivery falls on a Saturday, Sunday or public holiday, then data messages that have not yet been opened by the user will not be automatically delivered and the last day of the delivery fiction period will be the next working day at the earliest.
The most common problem occurs when people do not check their mailbox for several days and in the meantime the deadline for appealing or completing documents starts to run. In some cases, the consequences can still be remedied, but you need to act quickly. If you have a problem, we will be happy to help and advise you.
How do I find out if someone has a datacard and what kind of datacard?
Mailboxes provide a fairly detailed system for searching for recipients, so that you can find a person even if you are not sure, for example, exactly how to spell their name.
In addition to entering the name and surname, it is also possible to enter the personal (business) number of the person, or enter the address ( registered office or residence) and select from a list of names associated with the address. Of course, it is also possible to enter the mailbox ID itself, but this must be noted due to the difficulty of remembering.
Practice shows that problems often arise due to incorrectly selected addressee. Particularly in the case of municipal districts, contributory organisations or schools, the official name is often different from the commonly used designation.
For example, when entering the term “office of Prague 6”, the system offers 11 possible offices such as the customs office, the military office or the labour office, but none of them is an official office of the municipality. If you want to find one, you need to enter “Municipal district Prague 6”.
In these cases, where the commonly used term does not match the official name of the office, it is then worth going directly to the institution’s website first and then entering the address “for sure” in the data box.
Where and how do I manage my mailbox?
You can manage your mailbox simply on the My mailbox portal (mojedatovaschranka.cz). After logging in – for example, via eObčanky, Bank Identity or NIA – you will have access to all documents received and sent.
In addition to reading messages, you can also use the data mailbox portal to:
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Submit documents to authorities and courts,
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Archive important messages,
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Manage authorised persons (e.g. accountants),
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Set up notifications or message forwarding,
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Download delivery notes as evidence.
Why set up a data box even as a non-business owner?
Although a data box is still optional for ordinary individuals, many people set one up voluntarily – mainly for speed, clarity and the ability to deal with official business online. You can easily file a tax return, file an appeal or request a criminal record through “my mailbox“.
It is free, online and takes a few minutes to set up. We particularly recommend it for parents who often handle official communications on behalf of children or the elderly. Electronic communication via the data box portal has become not only a common practice but also an advantage. If you already have a data box, we recommend checking it regularly or setting up email notifications. If you don’t have one yet, consider setting one up. In 2025, it’s more of a surprise if someone doesn’t have a “data box”.
Data mailboxes today fundamentally affect the course of administrative, tax and court proceedings. An error in delivery or a missed deadline can have very unpleasant consequences. If you are unsure of the correct procedure, contact our attorneys.
Summary
Data boxes are an integral part of communication between the authorities and businesses and legal entities, for whom they are compulsorily set up. Documents delivered to the mailbox are deemed to have been officially delivered – either at the moment of opening or at the latest on the tenth day after delivery (the so-called delivery fiction), and if the tenth day falls on a weekend or holiday, the deadline is postponed. The mailbox can be accessed via the My mailbox portal, where you can not only read messages, but also send them to the authorities, archive them or manage access permissions. In addition, the tax office requires electronic communication exclusively via the data box for all persons for whom it has been established by law. It is possible to search for recipients in the system by name, ID number or mailbox ID. Although individuals without a business are not obliged to have a mailbox, more and more of them use it voluntarily to save time and money when dealing with the authorities.
Frequently Asked Questions
What happens if I don't open my mailbox?
After 10 days, the document is deemed to have been delivered even if you have not read it.
Do I have to have a data box as a self-employed person?
Yes. A data mailbox is established by law for natural persons who are in business.
Can I cancel my business mailbox?
If you are still in business, usually not. In some cases, you can apply to be made inaccessible when you close your business.
Do fines go to the data box?
Yes. The authorities and courts can deliver fines, notices and decisions via the data mailbox.
Is the email notification legally binding?
No. The moment of delivery to the data box is decisive, not the delivery of the e-mail.
