Email Signature: What to Include and the Right Size

A good email signature is five short lines: your name, your job title, the company, one phone number and the website. For a joinery workshop, the lines under the name could read: Workshop manager, Example Joinery Ltd, 01632 960 123, www.example.co.uk.

A limited company adds one more line in small type. Company law asks for four details on its business letters: the registered name, company number, registered office address and where it is registered. A business email to a customer or supplier generally counts as a letter. If you add a logo, keep it no wider than 400 pixels and no taller than 100, within Google's guidance for Gmail.

What to include in an email signature

Include what helps the reader reply, call or check who you are, then stop. Here is the full signature for an invented joinery company, ready to copy and change.

[Full name]
[Job title]
Example Joinery Ltd
01632 960 123
www.example.co.uk

Example Joinery Ltd. Registered in Scotland, company number SC000000.
Registered office: 1 Example Road, Stirling [postcode].

The business and its details are made up. Ofcom keeps numbers from 01632 960000 to 960999 for television and radio drama, so the phone line reaches nobody.

Line	Why it is there	Common mistake
Name	Says who wrote, even in a forwarded thread	Writing it inside an image
Job title	Shows what you can answer or decide	Two titles and a department
Company	Ties the person to the business	Leaving the name to the logo
One phone number	One clear way to call	Office, mobile and fax on three lines
Website	Lets the reader check you	A long tracking link
Legal line	Required for limited companies	Leaving it to the website

Leave out favourite quotes, a row of social icons, promotional banners and long confidentiality notices. The law requires none of them. On a small screen, they push the reply further down.

One term causes confusion. A DKIM signature is not something you write. It is a hidden code your sending server adds to each message, so the receiving server can check that nothing changed on the way.

Email signature legal requirements in the UK

A UK limited company has to put four details on its letters, order forms and websites. The rules do not mention email by name.

The regulations cover each type of document "in hard copy, electronic or any other form" (regulation 29(c)), so an email that does the job of a business letter is treated as one. The registered name goes further: it belongs on all business correspondence (regulation 24).

The rules are the Company, Limited Liability Partnership and Business (Names and Trading Disclosures) Regulations 2015, made under section 82 of the Companies Act 2006.

Detail	Example	Where the rule is
Registered name, exactly as on the register	Example Joinery Ltd	Regulation 24
The part of the UK where the company is registered	Registered in Scotland (or England and Wales, or Northern Ireland)	Regulation 25
Company number	SC000000	Regulation 25
Registered office address	1 Example Road, Stirling [postcode]	Regulation 25

All four are in Part 6 of the 2015 Regulations. The government lists the same details in its guidance on company stationery.

The registered office can differ from the place you work. Copy it from your Companies House record, not from your letterhead.

Two more rules apply only to extra lines. If the signature names a director other than the person signing, it must name every director (regulation 26). If it mentions share capital, it must give the paid-up figure (regulation 25(3)).

The details must be readable with the naked eye (regulation 20).

Breaking these rules without a reasonable excuse is an offence by the company and by every officer in default (regulation 28). The fine goes up to level 3 on the standard scale.

Level 3 is £1,000 in every part of the UK. The scales sit in the Sentencing Act 2020, the Criminal Procedure (Scotland) Act 1995 and the Fines and Penalties (Northern Ireland) Order 1984. A daily fine of up to a tenth of that can follow while the breach goes on.

Some signature guides still quote the Companies (Trading Disclosures) Regulations 2008. Those were revoked when the 2015 rules came into force on 31 January 2015 (Schedule 6).

Sole traders and partnerships have a shorter rule. It applies if you trade under a name that is not your own. Your business letters, invoices and receipts must then show your own name and a UK address where documents can reach you. In a partnership, that means every partner's name (Companies Act 2006, sections 1201 and 1202).

These rules decide what an email shows. Who you may send marketing to falls under a separate law, the Privacy and Electronic Communications Regulations (PECR). Its consent and soft opt-in rules are explained in UK GDPR and PECR for email.

This section summarises legislation.gov.uk as of 25 October 2026. It is not legal advice, and regulated professions may have extra wording to add.

Email signature size: width, logo and file weight

Keep the email signature narrow and the logo small, in pixels and in kilobytes (KB). Google recommends a signature image 70 to 100 pixels high and 300 to 400 pixels wide. The largest it allows is 1,000 pixels wide by 100 high (Gmail Help).

Gmail also caps the whole signature at 10,000 characters, and Google notes that an image counts towards that limit (Gmail Help). Both pages read this way on 25 October 2026.

Pixels are easy to see; weight is not. So we built one signature three ways and measured the HTML (the code behind a formatted email) and the whole reply as sent.

The stand-in logo was our own wordmark in PNG, the usual image format for logos. It has a transparent background and is 1,026 × 154 pixels as designed. We resized it to 400 × 60: a wordmark this wide reaches 400 pixels across before it is 70 pixels tall.

Version	Signature HTML	Whole reply as sent
Text only	518 bytes	1.4 KB
Text and a logo linked from a web address	684 bytes	1.5 KB
Text and an embedded logo, 400-pixel file (9.1 KB)	12.8 KB	14.3 KB
Text and an embedded logo, original file (13.2 KB)	18.3 KB	20.0 KB

Method: the reply is one line of text with a plain-text copy, built with Python's email library, and 1 KB is 1,000 bytes.

In the HTML column the logo sits in the code as base64 text, a form Gmail does not display; in the sent reply it travels as a separate inline part. Base64 is a third longer than the file, and the message adds line breaks and headers on top.

Linked or embedded logo

A linked logo stays on your web server, and the reader's mail app fetches it when the email opens. It adds almost nothing to the message.

The catch is picture blocking. Classic Outlook blocks automatic picture downloads by default, so a reader using it may first see an empty box (Microsoft Support).

An embedded logo travels inside every message, so it needs no download click. Its cost grows in long threads if each reply keeps the pictures of the messages it quotes.

In that worst case, the 20th email in a thread carries 20 copies of our 400-pixel logo, or 256 KB of pictures. Twenty copies of the text-only signature weigh 10 KB. We did not test which mail apps do this.

Whichever you choose, keep the number and the legal line as text. Give the logo alt text, the short description a mail app shows when a picture does not load. Export it at the width you show it: our resized copy was 4 KB lighter than the original file.

How to add an email signature in Outlook

New Outlook for Windows, Outlook on the web and Outlook.com use the same steps (Microsoft Support):

1. Select Settings, then Accounts > Signatures.
2. Select Add signature and give it a name.
3. Type or paste the signature into the box, then set the font and colour.
4. Use the checkboxes to add it to new messages, to replies and forwards, or both.
5. Select Save.

In classic Outlook, go to File > Options > Mail > Signatures and choose New. Set the default under New messages and under Replies/forwards. A logo goes in with the Image button in the signature editor.

Microsoft notes that an email signature saved under "Signatures on this device" stays on that computer. If you also use Outlook on the web or a second computer, set it up there too.

How to add an email signature in Gmail

In Gmail, the signature lives on the full settings page, set from a computer (Gmail Help):

1. Open Gmail, select Settings, then See all settings.
2. In the Signature section, add your signature text to the box.
3. Choose the signature defaults for new emails and for replies.
4. Select Save changes at the bottom of the page.

For a logo, Gmail takes a picture from a web address, from Google Drive or as an upload from your device. A Drive image shows only if anyone with the link can view it (Gmail Help).

The Gmail app for Android and iPhone has its own Mobile signature setting, which takes the text you type. If you never set one, the app uses the signature from your computer.

What breaks on mobile and in dark mode

A signature that looks fine in settings can break in four places.

• Narrow screens. A logo on the left and text on the right squeezes on a phone. One column, with the logo above or below the text, reads the same everywhere.
• A second device. A phone app or another copy of Outlook can send a different or older signature. Check each place you send from.
• Folded threads. In Gmail, the signature can sit behind the three-dot Show trimmed content button. Never put a deadline or other must-read detail only in the signature.
• Dark backgrounds. A signature logo is small, so a transparent one with black lettering, like ours, simply disappears on a dark reading pane. Save the signature copy of the logo with a white box behind the lettering.

Email signature or footer in marketing emails

In a newsletter or any marketing email, the footer does the legal work, not a person's signature. PECR regulation 23 forbids marketing emails that hide who sent them or give no valid address for opt-out requests (legislation.gov.uk).

So the footer names the sender and carries the unsubscribe link, as the last block of any newsletter layout. A limited company's newsletter is safest with the company-law lines from the section above as well. An owner's sign-off can still close the email, kept to a name and a role.

In the MailGraf email editor, the footer takes its address from your company details under Settings > Billing. MailGraf rebuilds that block when it sends, so a change there reaches every email you send afterwards. MailGraf's footer has no company number field, so put that line in a Text block just above it (Get to know the email editor).