Your digital mailbox
for e-invoices

A digital mailbox is a certified delivery service provider that ensures the secure sending and receiving of electronic invoices over the Peppol network. Under Act 385/2025, every VAT payer in Slovakia must use a digital mailbox to send e-invoices from 1 January 2027. Non-VAT payers must at minimum be able to receive e-invoices through a digital mailbox.

A digital mailbox acts as a certified intermediary — a so-called Peppol Access Point. Think of it as a courier for electronic invoices: it verifies the invoice format, encrypts the content, and securely delivers the document to the recipient. Without one, B2B invoicing will not be legally possible from 1 January 2027. Find out more about what a digital mailbox is and why you need onein our detailed article.

Unlike ordinary email services or cloud storage, a digital mailbox is not just a file forwarder. It is a regulated and audited participant in the Peppol network that must meet strict technical and security standards set by OpenPeppol and the national authority (in Slovakia, this is the Financial Administration). Every digital mailbox undergoes a certification process verifying its ability to correctly process, validate, and deliver electronic invoices in compliance with the Peppol BIS specification.

An e-invoice is not a PDF

The key difference between a standard invoice and an e-invoice is that an e-invoice is not a PDF or a scan of a paper invoice. An e-invoice is a structured XML/UBL file processed automatically — a computer reads it directly without manual data entry. This means fewer errors, faster processing, and full automation of accounting. Read a detailed comparison in E-invoice vs PDF — what's the difference?

A PDF invoice is essentially an image — the human eye can read it, but accounting software cannot process it without OCR. Moreover, OCR is not error-free: poor scan quality or non-standard data layouts cause mistakes that an accountant must fix manually. An e-invoice in UBL/XML format eliminates this problem entirely — data is structured, unambiguous, and machine-readable. That is why Act 385/2025 stipulates that from 1 January 2027 PDFs will only be accepted for B2C transactions.

How the Peppol network works — the 5-corner model

The Peppol network uses the so-called 5-corner model. The participants are: (1) the senderof the invoice, (2) the sender's digital mailbox (Access Point), (3) the SMP (Service Metadata Publisher — the register used to look up recipients), (4) the recipient's digital mailbox and (5) the recipient of the invoice. As a business you only interact with your own digital mailbox — the network handles everything else automatically. Learn more about the Peppol network and how it works in Slovakia in the Peppol in Slovakia guide.

In practice it looks simple: your business creates an invoice in your accounting software. The digital mailbox (in this case ePošťák) picks it up, validates it against Peppol BIS 3.0 rules, looks up the recipient in the SMP register and delivers the invoice to their digital mailbox, which then delivers it to the recipient. The whole process takes seconds. The fifth 'corner' of the model is the Financial Administration, which has access to transaction data in near real time — ultimately replacing the VAT control statement.

Why was it introduced?

Mandatory e-invoicing stems from the European ViDA (VAT in the Digital Age)directive, which aims to digitise tax processes across the EU. The European Commission estimates that VAT fraud costs EU member states more than €60 billion per year. Structured e-invoicing through the Peppol network will allow tax authorities to access transaction data in real time, making fraudulent schemes significantly harder. Slovakia implemented this obligation through Act 385/2025 with effect from 1 January 2027. The goals are to reduce tax fraud, speed up business transactions, and modernise accounting.

The ViDA directive also envisages that by 2030 e-invoicing will be mandatory for cross-border transactions across the entire EU. Slovakia is among the first countries to introduce a national implementation. Other member states (France, Germany, Poland) are preparing their own timelines. For Slovak businesses trading internationally, this means the investment in a digital mailbox pays off even more — the same infrastructure will serve cross-border invoicing as well.

Digital mailbox vs invoicing software

Invoicing software (e.g. POHODA, SuperFaktúra, iDoklad) is used to create an invoice. A digital mailbox is used for its secure delivery over the Peppol network. They are two different things that complement each other. Your invoicing software creates the invoice; the digital mailbox delivers it to the recipient. Some digital mailboxes (including ePošťák) offer an API integrationthat allows connection to any invoicing system.

A common misconception is that 'if I have accounting software, I don't need a digital mailbox.' This is not true — your accounting software creates the invoice but has no authorisation to deliver it via Peppol. For that you need a certified mailbox. Some large accounting packages are gradually building connections to digital mailboxes — in that case the integration will be transparent and you simply choose which mailbox to use. For smaller software and custom solutions the best path is direct ERP integration via API.

Not all digital mailboxes are the same. Several certified providers operate in Slovakia and their services differ in price, features, support quality, and technical capabilities. Choosing the right mailbox saves you time, money, and headaches for years to come. Focus on these criteria (covered in depth in our article How to choose a digital mailbox):

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  Price and transparency

  Compare the monthly fee and the per-invoice price for sending and receiving. Some providers charge per invoice; others offer flat-rate plans. Watch out for hidden fees for archiving, API calls, or data exports. ePošťák offers free receiving and transparent pricing from €0/month.

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  API and integrations

  If you use accounting software (POHODA, Money S3, SuperFaktúra) or a custom ERP, you need an API. Manually downloading invoices becomes unmanageable at even a few dozen documents per month. Check whether the provider has a documented REST API, a sandbox for testing, and webhook support.

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  Customer support and SLA

  A digital mailbox provider is critical infrastructure — if it goes down, you cannot invoice. Verify that the provider communicates in your language, has a defined SLA with uptime guarantees, and is reachable on business days at minimum. Ideally look for a provider guaranteeing 99.9% uptime.

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  Certification and reliability

  Only choose certified providers registered with the Financial Administration. Also verify their OpenPeppol membership and service availability history. An uncertified mailbox cannot legally deliver e-invoices.

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  Liability

  What happens if the mailbox fails and you miss an invoice deadline? Check the terms and conditions and the scope of the provider's liability. A quality mailbox has clearly defined responsibility for outages and provides logs as evidence for tax authority audits.

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  Sandbox environment

  Before going live you want to test the system. Check whether the mailbox offers a sandbox (test environment) where you can try sending and receiving invoices without real-world consequences. ePošťák's sandbox is free for all plans.

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  Additional features

  Telegram integration, multi-client management, cost calculator, Peppol Directory — these features save time and simplify your workflow. Not every mailbox offers them.

Transparent pricing with no hidden fees. Receiving e-invoices is always free. Choose a plan based on how many invoices you send per month: