Digital signature in the lease agreement: When the qualified electronic signature is mandatory

Problem: A fixed-term lease agreement that is digitally signed with the wrong signature level is formally invalid and, according to § 550 of the German Civil Code (BGB), is deemed to have been concluded for an indefinite period.

Cause: Many property managers assume that any form of digital signature is equivalent, but signature law distinguishes three levels with significantly different legal effects.

Thesis: Only the qualified electronic signature (QES) meets the statutory written form requirement according to §126a BGB, which is why a signature workflow is needed that recognizes the contract type and applies the appropriate level.

When the Qualified Electronic Signature is Mandatory in a Lease Agreement

Direct Answer: Open-ended lease agreements are form-free and can be legally concluded with any e-signature level. Fixed-term lease agreements for more than one year (§ 575 BGB), stepped rent agreements, and index-linked rent agreements are subject to the statutory written form requirement. This can only be met digitally by a qualified electronic signature (QES) according to §126a BGB in conjunction with the eIDAS Regulation.

The Misunderstanding: "We already sign digitally"

Many property managers assume that any form of digital signature is equivalent. This is a misconception with potential legal consequences. Signature law distinguishes three clearly defined levels, which differ significantly in security level and legal effect.

2.1 Simple Electronic Signature (SES)

The SES is the lowest level. This includes a scanned signature as an image file in a PDF, a typed name at the end of an email, or a checked box in an online form. There is no technical link between the signature and the signer. The SES offers no statutory protection and cannot replace the written form requirement.

2.2 Advanced Electronic Signature (AES)

The AES is technically more secure than the SES. It is uniquely assigned to the signer, was created under their sole control, and reliably detects subsequent changes to the signed document. Typical fields of application are internal approvals and contracts without a statutory written form requirement. However, the AES is unsuitable as a digital substitute for the written form according to § 126a BGB.

2.3 Qualified Electronic Signature (QES)

The QES is the legally strongest type. It is based on a qualified certificate from an accredited Trust Service Provider (TSP) and meets the statutory written form requirement in accordance with § 126a BGB. It is recognized in all EU member states according to the EU Regulation eIDAS (910/2014) and is therefore effective across borders. Only the QES can fully replace the handwritten signature legally in form-bound contracts.

What Happens with the Wrong Signature Level

A fixed-term lease agreement that is not signed via QES is deemed formally invalid. The legal consequence is regulated in § 550 BGB: A lease agreement concluded for a specific duration without complying with the statutory form is deemed to have been concluded for an indefinite period. The agreed fixed term has no effect. Both contracting parties can terminate the agreement with the statutory notice period, regardless of the originally intended term.

For owners who rely on a specific return date (for example, in the case of plans for personal use with a specific moving-in date), this is a significant risk. The fixed-term contract without QES does not protect them legally.

The formal defect does not have to be immediately recognizable. Both sides can fulfill a formally invalid contract for years without contesting it. The risk only comes to light when one party no longer accepts the fixed term and insists on ordinary termination.

Which Lease Agreement Requires Which Signature Level

Not every lease agreement has the same requirements. The decisive factor is whether there is a statutory written form requirement:

Open-ended lease agreement

• Written form requirement: No (form-free)

• Minimum signature level: SES or AES sufficient

Fixed-term lease agreement over 1 year (§ 575 BGB)

• Written form requirement: Yes

• Minimum signature level: QES required

Stepped rent lease agreement (§ 557a BGB)

• Written form requirement: Yes

• Minimum signature level: QES required

Index-linked rent lease agreement (§ 557b BGB)

• Written form requirement: Yes

• Minimum signature level: QES required

For open-ended lease agreements, property managers can resort to simpler signature levels without taking legal risks. For all contract types with a statutory written form requirement, however, the QES is the only permissible digital way.

Identification with the Trust Service Provider

The QES requires prior identification of the signer with the Trust Service Provider. The process is standardized: The signer authenticates themselves via a two-factor process, usually via video identification or with the German eID identity card. Based on this identification, the Trust Service Provider issues a qualified certificate that is uniquely and permanently linked to the identity of the signer.

Cryptographically Secured Signature Process

The actual signature process is cryptographically secured. Subsequent changes to the document are recognizable because the signature is bound to the exact document state at the time of signing. Any subsequent change invalidates the signature.

EU-wide Validity according to eIDAS

This process corresponds to the technical and legal requirements of the eIDAS Regulation (EU 910/2014). The regulation applies directly in all EU member states: A QES from a German accredited provider is also legally valid in other EU countries, which can be relevant for cross-border leases.

Archiving Signed Contracts in an Audit-Proof Manner

The process is not complete with the signature. Signed lease agreements must be stored unalterably, completely, and in a retrievable manner throughout the statutory retention period. This is required by the Principles for the Proper Keeping and Preservation of Books, Records, and Documents in Electronic Form (GoBD). Unalterability means: A stored document must not be changed without the system automatically logging this process with a timestamp.

Plan for Retention Periods

For lease agreements and associated correspondence, a retention period of six years applies according to § 257 of the German Commercial Code (HGB). If a document also serves as an accounting voucher, the period is eight years; ten years apply to commercial books, inventories, and annual financial statements. Archiving is not an optional extra, but a prerequisite for verifiability in the event of a dispute. How this proof is structured in detail and which gaps frequently arise in practice is explained in the article on audit-proof documentation in property management.

Conclusion

Not every lease agreement requires a QES. However, anyone who wants to digitally conclude fixed-term leases, stepped rent, or index-linked rent agreements cannot avoid the QES. An incorrectly chosen signature level makes the fixed-term contract formally invalid and converts it by law into an open-ended lease. Property managers who want to rule out this risk need a signature workflow that recognizes the contract types and automatically applies the appropriate signature level.

More on the topic: auditable renting process.

Download Buyer's Guide Compliance-Readiness (Section Signature Requirements) | Request demo to see the signature workflow in EverReal.

Note on Legal Context

The QES makes the signing of the contract legally secure in the sense of the statutory written form requirement according to § 126a BGB. The validity of the overall contract also depends on other factors, in particular on the contract content, the correct rent amount, and compliance with tenancy law regulations. For individual questions regarding contract design, we recommend consulting a lawyer specializing in tenancy law or contacting professional associations such as VDIV or IVD.

We do not provide legal advice. Property managers are advised to clarify specific legal questions with a specialist lawyer or their association (VDIV, IVD).

Q: Can I send a lease agreement as an email attachment with a simple signature?

A: For open-ended lease agreements, this is generally possible since they are form-free and do not require a specific signature level. However, for fixed-term lease agreements over one year (§ 575 BGB), stepped rent, and index-linked rent agreements, the statutory written form requirement applies. A scanned signature as an email attachment does not meet this requirement. In these cases, a qualified electronic signature (QES) according to § 126a BGB is legally necessary.

Q: What is the difference between SES, AES, and QES?

A: The simple electronic signature (SES) includes any digital identification of the signer without a technical link to their identity, for example, a typed name or a scanned signature. The advanced electronic signature (AES) is technically more secure, uniquely assigned to the signer, and detects subsequent manipulation of the document, but is not considered a statutory substitute for the written form. The qualified electronic signature (QES) requires identification with an accredited Trust Service Provider, is based on a qualified certificate, and is the only digital substitute for a handwritten signature in form-bound contracts according to § 126a BGB.

Q: When does a fixed-term lease agreement without QES become invalid?

A: A fixed-term lease agreement (temporary lease under § 575 BGB) that does not meet the statutory written form requirement is deemed to have been concluded for an indefinite period according to § 550 BGB. The fixed term has no effect, and both parties can terminate the agreement with the regular statutory notice period. A digitally signed fixed-term lease agreement without a QES carries this risk from the very beginning, regardless of whether the formal defect is noticed months or years later.

Q: Must the QES be used by both parties (landlord and tenant)?

A: Yes. The written form requirement according to § 126 BGB requires the handwritten signature by all contracting parties on the same document. The digital substitute according to § 126a BGB accordingly requires that all contracting parties, i.e., both landlord and tenant, sign the contract with a QES. A unilateral use of the QES by only one party is not sufficient to meet the written form requirement for the overall contract. Trust Service Providers integrated into signature workflows usually support the multi-party signing process.