Email signatures: the mandatory details for businesses

The law does not define the business letter by paper, letterhead or signature, but by two features: it comes from the business, and it is addressed to a specific recipient. For merchants, the rule says the details must appear on all business letters “whatever their form” (Section 37a HGB). The same wording appears in the GmbH Act (Section 35a GmbHG), the Stock Corporation Act (Section 80 AktG), the Cooperatives Act (Section 25a GenG) and the provision for general and limited partnerships (Section 125 HGB). An email with a quote, the reply to a customer enquiry, the email that sends an invoice, or a query to a supplier about a delivery date: these are as a rule business letters within the meaning of these provisions.

That emails are included is not a recent interpretation. The words “whatever their form” entered the provisions with the Act on Electronic Commercial Registers and Cooperative Registers and the Company Register, known as the EHUG. In its bill, the Federal Government wrote that the details already required on business letters would in future also apply to email correspondence (Bundestag printed paper 16/960). The explanatory memorandum also points out that the prevailing view in legal literature already regarded faxes and emails as covered; the amendment was therefore a clarification. Anyone who maintains the details on printed letterhead and leaves them out of the signature fulfils the duty for paper only.

The law names one exception, and it is narrower than it sounds. No details are needed for communications or reports issued within an existing business relationship for which pre-printed forms are customarily used, so that only the particulars of the case have to be filled in (Section 37a HGB). This means form letters within an ongoing customer relationship, not the freely written email to a new prospect. For order forms the law expressly withdraws the exception: they count as business letters even when sent as a pre-printed form (Section 37a HGB). Because day-to-day email rarely allows a clean line between messages that fall under the exception and those that do not, the practical conclusion is simple: the details go into every business signature, without case-by-case decisions.

Who is not covered? The provisions address merchants and companies entered in a register, that is the commercial, cooperative or partnership register. Small traders and freelancers without an entry have neither register court nor register number to state. For them, the website legal notice (Section 5 DDG) and the mandatory invoice details (Section 14 UStG) remain the relevant rules. Whether a business ought to be registered as a merchant is a separate question; it belongs with the tax adviser or the chamber of commerce, not in the signature template.

A sole merchant entered in the commercial register states the company name, the designation “eingetragener Kaufmann” or “eingetragene Kauffrau” or a generally understood abbreviation such as e.K., e.Kfm. or e.Kfr. (Section 19 HGB), the place of business, the register court and the number of the entry (Section 37a HGB). If the signature only shows the owner’s name and a phone number, that is not enough for a registered merchant. The place of business is where the business is run, as entered in the register, not the owner’s home town.

For a GmbH, the law requires the legal form and seat of the company, the register court of the seat, the number of the commercial register entry and all managing directors (Section 35a GmbHG). If the company has formed a supervisory board and the board has a chair, the chair belongs there too. The persons are named with their surname and at least one first name written out (Section 35a GmbHG). “E. Mustermann” is therefore not enough, “Erika Mustermann” is. Section 35a does not list the company name itself; it appears as the sender above the register lines anyway.

Two points are easily missed. First: all managing directors, not only the person writing the email and not only the one in overall charge. Appointing a second managing director therefore changes the signature of every person in the business. Second: share capital does not have to appear in the signature. Anyone who does state it must give the share capital and, if not all cash contributions have been paid in, also the total amount of outstanding contributions (Section 35a GmbHG). A capital figure without this addition is worse than none when contributions are outstanding.

The following signature of a fictitious GmbH with two managing directors shows how this fits together. Names, register number and phone number are placeholders. The addresses end in .invalid, a domain intended for names that are obviously invalid (RFC 2606); it belongs to nobody.

The upper lines are what every sender adds anyway: name, role, company, contact. The three lower lines are the duty. “Registered seat” is the place stated in the articles of association and the register, not necessarily the workshop address. Which local court keeps the register is shown in the register extract. It is not automatically the court in your own town: the local court at the seat of the regional court is generally responsible for that court’s whole district, and the federal states may allocate the registers differently (Section 376 FamFG). Copy the register number with the prefix shown in front of it in the extract, such as HRB.

For a UG only the company line changes: “Beispielbetrieb Haustechnik UG (haftungsbeschränkt)”. For a registered merchant the management line is dropped; instead of “Registered seat” the place of business is stated, and the company name carries the suffix e.K. A GmbH & Co. KG adds a second block, for example “Personally liable partner: Beispielbetrieb Verwaltungs-GmbH, seat Hildesheim, Amtsgericht Hildesheim, HRB 00000, managing director: Erika Mustermann”. Section 35a GmbHG does not require a postal address; for queries and returns it usually belongs there all the same.

The signature in the main desk mailbox is as a rule set up. Gaps appear at the edges, where emails are sent from another program, another device or automatically. For the duty this makes no difference: it attaches to the business letter, not to the program it comes from.

To find the gaps, send yourself one email from every route: from the office PC, the smartphone, the browser, as a reply, as a forward, from every shared mailbox, from the shop and from the accounting software. Whatever arrives in your own inbox without a register line arrives the same way at the customer’s. The test is quick and reveals the gaps that otherwise only a customer notices.

There are two ways to keep the signature consistent across several mailboxes. The simple one: a binding text template, stored centrally and distributed to everyone after each change, with short instructions per program and device. The technical one: some mail servers can append a text block to every outgoing message. That also reaches smartphones, but places the block below quoted threads and has to be coordinated with sender authentication. If a message is changed after DKIM signing, the check at the recipient can fail. How SPF, DKIM and DMARC work together is explained in Setting up professional email on your own domain.

In a typical business the same details appear in several places: on the letterhead, in every email signature, in the website legal notice and in the invoice templates. The legal bases differ. The legal notice requires, for legal entities, legal form and authorised representatives, the register including number and, where available, the VAT ID (Section 5 DDG). The invoice needs the tax number or the VAT ID (Section 14 UStG). The content overlaps so much, however, that a change in one place as a rule affects all the others.

A single master sheet with the company details is therefore practical: company name, legal form, seat, address, register court, register number, management, VAT ID. Every template, that is signature, legal notice, invoice footer and letterhead, is filled from this sheet. When something changes, change the sheet first and then every place in one pass. For the website, website maintenance can take care of this on request, for mailboxes and domain the fixed contact for web hosting. When a company is renamed, domain, mailboxes and quote templates hang on the same list; more in Business name and domain: check trademarks before you start.

The signature has a second life: in the archive. Business letters received and copies of those sent must be kept for six years (Section 147 AO); under commercial law the same period applies to commercial letters (Section 257 HGB). The period starts at the end of the calendar year in which the letter was received or sent (Section 147 AO). An email from December 2026 must therefore as a rule be kept until the end of 2032, and longer while it matters for a tax whose assessment period has not yet expired (Section 147 AO). A mailbox with a provider that ends with the contract is no archive for this; how to take mail stocks with you safely is covered in Moving domain and email without losing mail.

The turn of the year is a good moment for the comparison: invoice number ranges, letterhead and templates are often touched then anyway. If a change of owner is coming up, signatures, mailboxes and register details belong on the handover list; what that looks like is covered in Business succession: handing over website and customer data properly.