The Czech data box (datová schránka), explained in English
If you run a company in the Czech Republic, work here as a self-employed person, or simply live here, sooner or later someone will ask for your data box ID or tell you that a letter “was delivered to your data box”. The data box is the official electronic mailbox of the Czech Republic — and mail in it has real legal consequences even if you never open it. This guide explains the essentials in plain English.
What a data box is
A data box (datová schránka) is an electronic mailbox run by the Czech state in its Data Box Information System (ISDS), set up under Act No. 300/2008 Coll. It is not e-mail: you cannot write to it from Gmail, and it does not forward anything to your inbox. Messages travel only between data boxes, each one with an electronic seal and a qualified time stamp, so it is always provable who sent what and when.
Public authorities — tax offices, courts, the social security administration, municipalities — are required to send documents to your data box if you have one, instead of sending paper letters. Companies and individuals can also send each other messages through it; these are called poštovní datové zprávy (PDZ).
Every box has a public seven-character ID (for example abc1234). The ID is an address, not a login: you give it to people who need to send you something, and you can look up anyone’s ID in the public list of data box holders.
Who has one by law
The state sets up a data box automatically, without any application, for:
- legal entities entered in the Czech register of persons — this includes companies such as an s.r.o. or a.s., whoever owns them;
- self-employed individuals (podnikající fyzické osoby) entered in that register — e.g. anyone with a Czech trade licence;
- certain professions, such as lawyers, tax advisers, insolvency administrators, statutory auditors, court experts, sworn translators and interpreters, and authorised architects and engineers;
- public authorities.
Companies in the Commercial Register have had a box since the system started in July 2009. Since 1 January 2023 (Act No. 261/2021 Coll.), every legal entity in the register of persons — including associations and foundations — and every self-employed individual gets one automatically as well.
Private individuals — Czech citizens and foreigners alike — can get a personal data box on request: at any Czech POINT office (the state’s contact points, found at many post offices and municipal offices), or online after signing in with the state’s digital identity (Identita občana). A personal box is voluntary; once you have one, however, authorities will use it.
Foreign-owned company? It already has a box.
A Czech subsidiary is a Czech legal entity, so its data box exists whether or not anyone has ever logged in — and mail sent to it still takes legal effect (see the 10-day rule below). The login details go to the statutory representative (for an s.r.o., the jednatel): to their Czech address from the population register if they are identified there, otherwise to the permanent address recorded in the Commercial Register. If nobody knows where those details are, see the FAQ.
When mail counts as delivered: the 10-day rule
Czech law distinguishes two moments:
| Term | What it means |
|---|---|
| Arrived (dodáno) | The message has reached your data box — like a letter dropped into your letterbox. Nothing has legal effect yet. |
| Delivered (doručeno) | The moment the message takes legal effect and deadlines (for an appeal, a payment, a reply) start to run. |
A message is delivered as soon as someone with access to it logs in to the data box (Section 17(3) of Act No. 300/2008 Coll.). If nobody logs in, it is deemed delivered on the tenth day after it arrived — whether or not anyone has read it. Czech lawyers call this the fikce doručení (deemed delivery). Since 2022 the same 10-day rule also applies to PDZ messages between companies and individuals.
Not logging in does not protect you
Ignoring the data box only postpones delivery to day ten. A tax assessment, court order or fine sent to an unattended box is legally delivered all the same, and the deadlines run from that day. How weekends and public holidays affect day ten depends on who sent the message; our deemed-delivery calculator (in Czech) works out the exact date.
Logging in through any app counts too: a third-party app delivers your pending messages when it downloads the list of received messages. That is also why no data box app can safely alert you to new mail in the background — checking for it would itself deliver the mail and start the deadlines. To be notified, set up e-mail notifications (free) or SMS notifications (paid) in the settings of the official portal.
Messages are deleted after 90 days
The data box is a mailbox, not an archive. The system keeps a message for 90 days from the moment it was delivered by someone logging in; then the message and its attachments are deleted for good. Only a record of the “envelope” (sender, recipient, subject, times) is kept. A message that nobody has ever opened by logging in is kept for at least three years.
So download anything you may need later — contracts, decisions, tax documents — as a ZFO file or PDF. The state also sells a paid long-term storage add-on, the data vault (datový trezor).
How to log in
The official web portal is mojedatovaschranka.cz. You can log in with the username and password you received when the box was set up, and you can add an SMS code or other second factor. If you have a Czech digital identity (Identita občana, e.g. via your bank), you can use it on the portal instead of a password. Signed in that way, you cannot change your password, but you can cancel your login details and issue yourself new ones.
The first username and password are valid for one login only — the system asks you to set your own password straight away. Third-party apps connect with a username and password (optionally with a second factor); the Czech digital identity works on the web portal only.
We describe every login method, with what to do when you are locked out, in our data box login guide — it is in Czech, but works well with your browser’s translate function.
ZFO files
When you save a message from the data box, you get a file ending in .zfo. It contains the whole message — sender, recipient, times of dispatch and delivery, and all attachments — sealed by the system so that its authenticity can be verified later. Ordinary programs cannot open it. Our free online ZFO viewer (Czech interface) shows the content and lets you save the attachments; the file is processed in your browser and never uploaded.
Sending a file yourself? Only certain formats are allowed, and a standard message may be about 20 MB in total, envelope included, so leave some headroom. Our attachment checker (Czech interface) tests your files before you send them.
Practical tips
- Check the box regularly — at least once every ten days, so that nothing is delivered “behind your back”.
- Turn on e-mail notifications in the portal settings, so you know when something arrives.
- Give someone access. The box holder (or the company’s statutory representative) can create separate logins for an accountant or office manager — so-called authorised persons (pověřené osoby) — with limited rights, via the portal or at Czech POINT. Remember that their login delivers the messages they have access to, exactly like yours.
- Save important messages before the 90 days are up.
- Watch your password’s expiry date. By default your password expires after 90 days; you can switch expiry off in the portal, at your own risk. Change it in time, or apps that sign in with it will stop working.
- Lost login details? Any Czech POINT office can cancel them and issue new ones.
Frequently asked questions
Does my Czech company have a data box even if I never set one up?
Yes. Legal entities entered in the Czech register of persons, such as an s.r.o. or a.s., have a data box set up automatically by law (for all of them since 1 January 2023), and messages sent to it are deemed delivered after ten days even if nobody logs in. The login details are sent to the statutory representative.
What happens if I never log in to my data box?
Messages are deemed delivered on the tenth day after they arrive in the box, and all legal deadlines run from that day. Not logging in does not stop delivery — it only delays it to day ten.
Can I get a data box as a foreigner?
Yes. Any individual can ask for a personal data box, for example at a Czech POINT office. Identification is primarily checked against the Czech population register. If you run a business registered in the Czech Republic, that business already has a box by law.
How long are messages kept in the data box?
90 days from delivery by logging in; after that the message and its attachments are deleted and only the envelope record remains. Save anything important as a ZFO file or PDF, or use the paid data vault (datový trezor).
Is the Mobilní Datovka app available in English?
No — the app is in Czech only, like most data box software. The key terms on this page, dodáno (arrived), doručeno (delivered) and fikce doručení (deemed delivery), are the ones you will see most often.
We lost the login details for our company’s data box. What now?
The statutory representative can ask for the old details to be cancelled and new ones issued: in person at any Czech POINT office, by post with a certified signature, by a request sent from another data box (e.g. their personal one) to the system administrator’s box, or on the portal after signing in with the Czech digital identity.
Your data box on your phone
Mobilní Datovka is an independent app for iPhone and Android. It keeps your personal, business and company boxes in one place and saves a copy of your messages and attachments on your phone, so they survive the state’s 90-day deletion (browsing that archive is part of the paid Plus subscription). Please note: the app is in Czech only, and — because of the 10-day rule above — it never checks for new mail in the background.
This page is general information, not legal advice. It is based on Act No. 300/2008 Coll. and the ISDS operating rules (Provozní řád ISDS) valid from 17 April 2026. Mobilní Datovka is an independent ISDS client; it is not an official state app and is not affiliated with the administrator or operator of ISDS.