UK legal requirements for business email signatures
What a limited company, a sole trader or a partnership has to put in an email, what is only habit, and how to make sure every mailbox in a Microsoft 365 tenant complies.
This is general information, not legal advice. The law is quoted from legislation.gov.uk and GOV.UK as they read on 15 September 2026; if your situation is unusual, ask a solicitor.
What limited companies must include
The Companies Act 2006 lets the Secretary of State require companies to disclose their name and other information on specified documents and communications (Companies Act 2006, s.82). The regulations made under it are the Company, Limited Liability Partnership and Business (Names and Trading Disclosures) Regulations 2015, and they set two tiers.
The registered name, everywhere. Regulation 24 requires a company to disclose its registered name on its business letters, notices, order forms, invoices, receipts, its websites, and “all other forms of its business correspondence and documentation” (Names and Trading Disclosures Regulations 2015, reg. 24). A business email is business correspondence, so the registered name, including “Limited” or “Ltd”, belongs in every one.
The fuller particulars on business letters, order forms and websites. Regulation 25 adds, for those three, the part of the United Kingdom in which the company is registered, its registered number, and its registered office address (Names and Trading Disclosures Regulations 2015, reg. 25). GOV.UK’s summary of the same rules is GOV.UK: signs, stationery and promotional material. Two further points from the same regulation and guidance:
- If you mention share capital, you must state how much is paid up.
- If a business letter names any director other than in the text or as the signatory, GOV.UK says you must list all of them.
The regulations do not use the word “email”. The registered-name duty in regulation 24 clearly covers it. Whether an email is a “business letter” for regulation 25’s extra particulars is the question most organisations answer by treating it as one, because the cost of including a company number and registered office is a line of text and the cost of omitting it is an argument. The safe signature for a UK limited company therefore carries:
- The full registered name, for example “Northwind Trading Limited”.
- The registered number.
- Where it is registered: England and Wales, Scotland, or Northern Ireland.
- The registered office address, which need not be the trading address.
Limited liability partnerships are covered by the same 2015 Regulations and the same particulars apply, with the registered office and number of the LLP.
Sole traders and partnerships
Chapter 2 of Part 41 of the Companies Act 2006 applies to an individual or partnership carrying on business in the United Kingdom under a business name, meaning a name other than the individual’s surname or all the partners’ surnames with only permitted additions (Companies Act 2006, s.1200). If that is you, the information required is the individual’s name, or the name of each partner, and an address in the United Kingdom at which service of any document relating to the business will be effective (Companies Act 2006, s.1201). It must appear on business letters, written orders, invoices, receipts and written demands for payment (Companies Act 2006, s.1202). Trading as “Jane Smith” with no business name takes you outside the chapter; trading as “Smith Plumbing” brings you into it.
Disclaimers: what’s required and what’s just habit
Most of what appears under a UK signature is not required by any of the above.
- Confidentiality notices (“this email is intended only for the addressee…”) are not required by companies law. They are a habit, and their legal effect on a recipient who never agreed to them is limited. Keep one if your legal team wants it; do not mistake it for compliance.
- “Views are my own” disclaimers likewise: optional.
- VAT numbers are required on VAT invoices (GOV.UK: VAT invoices), not on ordinary correspondence. Many companies include theirs anyway; that is a choice, not a duty.
- Regulated sectors can have their own requirements on top: a firm regulated by the FCA, a solicitors’ practice, a charity stating its registered charity number. Check the rules for your regulator rather than assuming the companies-law set is the whole list.
The useful distinction is between the particulars (name, number, place of registration, registered office), which are fixed by law and identical for everyone in the company, and the disclaimer, which is a policy decision. Keep the two in separate blocks so the legal one can be enforced and the other one can change.
Per-domain disclaimers for multi-brand tenants
One Microsoft 365 tenant often carries several legal entities: a group with subsidiaries, a firm that acquired another, an MSP-run tenant with two trading names. Each entity has its own registered name, number and office, and its people usually send from that entity’s email domain. The rule therefore has to be “the disclaimer for the domain the message is sent from”, not “one disclaimer for the tenant”. A transport rule can do this with conditions on the sender domain; a signature tool should let you attach a footer to a domain directly so nobody has to remember which template carries which entity.
Enforcing it across Microsoft 365
Whatever tool applies signatures, the compliance block should be something a template author cannot leave out. In Sigil that is a compliance footer: a legal block attached to an email domain and appended at render time, beneath whichever signature template the person was assigned. Marketing can change the design as often as it likes; the particulars for each entity stay where Legal put them. The features overview shows footers alongside templates, rules and banners, and managing Outlook signatures across Microsoft 365 explains the options, including the built-in Exchange Online mail flow rule, for organisations that only need the footer.