Adding the Mandatory Details to Business Letters and Emails

Anyone who sends business letters as a merchant or corporation must always include certain company details, and for years this has also applied to ordinary business emails, not just paper letters.

In brief: § 37a HGB (German Commercial Code) and § 35a GmbHG (German Limited Liability Companies Act) require merchants and corporations to state on every business letter, including emails, the company name, legal form, registered office, the register court with the register number and, for corporations, the names of all managing directors. If these mandatory details are missing, coercive fines and competition-law warning letters from competitors or associations are possible.

Who is affected by the obligation?

All merchants within the meaning of the Commercial Code (Handelsgesetzbuch) are affected, as well as corporations such as the GmbH, the UG (haftungsbeschränkt) and the AG. § 37a HGB and § 35a GmbHG expressly prescribe the mandatory details for them as soon as they send a business letter to a specific, named recipient; this expressly includes business emails, not just traditional paper mail. Anyone registered as a merchant in the commercial register is subject to the obligation, just like a multi-member management board of a GmbH. The rule therefore affects a large share of businesses, regardless of industry or company size.

Which details must appear on business letters and emails?

Every business letter must show the company name, legal form, registered office and the register court with the register number. For corporations, all managing directors or board members must additionally be named, not only the person who actually signs the letter. The following overview shows which detail is mandatory for whom:

These details belong in the email signature just as much as on letterheads, invoices and quotations. A tool such as Company Audit shows which of these obligations apply to your company in concrete terms.

Where exactly must the details appear?

The mandatory details belong in all outgoing correspondence addressed to a specific recipient, that is, letterheads, invoice templates, quotation templates and the email signature of all employees. Invoices and quotations sent as PDF attachments also count as business letters and require the complete details. Circulars to an unspecified group of recipients, such as general advertising mailings without specific addressing, are not covered by this obligation. In practice, however, this affects very few messages, since most business emails and documents are addressed to a specific contact person. In case of doubt, it is simpler to include the mandatory details in every template as a matter of principle, rather than checking case by case whether a specific recipient is involved.

What do you need to do in practice?

Implementation can be organised in a few clearly defined steps:

1. Compile the mandatory details: company name, legal form, registered office, register court and register number.
2. For corporations, additionally name all managing directors or board members.
3. Build the details into the email signature of all employees.
4. Add the details to letterheads, invoice templates and quotation templates.
5. When changes occur, such as new management or a change of registered office, update signatures and templates promptly.

A central signature template for all employees prevents individual mailboxes from forgetting the details or continuing to use outdated versions. If the template is maintained centrally and rolled out automatically, a single update is enough to bring all outgoing channels (email, letterhead, invoice and quotation templates) up to date at the same time.

What are the consequences of a violation?

If the mandatory details are missing on business letters or emails, the register court can impose a coercive fine to enforce compliance. In addition, competition-law warning letters from competitors or associations are possible, since incomplete mandatory details can be treated as a competition violation. Both risks can be avoided with manageable effort: anyone who sets up templates and signatures properly once and maintains them consistently with every organisational change keeps the mandatory details correct in the long term and noticeably reduces the risk of warning letters. Especially in growing teams, it is worth regularly checking all outgoing channels so that new employees work with the correct signature from the start.

Frequently asked questions

Does the obligation also apply to sole proprietors?

The obligation under § 37a HGB affects merchants within the meaning of the Commercial Code. Anyone registered as a merchant must include the details just like a corporation, regardless of how small the business is.

Does a business email count as a business letter?

Yes. § 37a HGB and § 35a GmbHG expressly cover business emails as well, not just paper letters. The mandatory details therefore belong in the signature of every business email sent to a specific recipient.

Do all managing directors have to be named?

For corporations, yes: all managing directors or board members must be named on the business letter, not only the person who signs it.

Does the obligation also apply to invoices and quotations sent as PDFs?

Yes. Invoices and quotations sent as PDF attachments also count as business letters and require the complete mandatory details, just like a traditional letter on paper.

What happens when the management changes?

Signatures, letterheads and templates must be updated promptly as soon as the management or registered office changes, so that the details on all business letters remain correct and complete.

Source: § 37a HGB · § 35a GmbHG. This article is general information and does not replace legal advice in an individual case. As of: July 2026.