Email signature best practices come down to fifteen rules, and every one of them exists because a mail app behaves in a particular way: Gmail caps the length, Outlook holds back pictures, plain text drops images, and a phone may show none of your formatting. Each rule below gives a bad example, a good one, and the reason.
The vendor facts come from Google’s and Microsoft’s own help pages, which we read in October 2026: Gmail’s signature page and Microsoft’s Outlook signature page. Where a rule is our own advice rather than a vendor limit, the text says so.
The 15 rules in one glance
- Words: one title, one number per purpose, short link text, four to seven lines.
- Build: tables, widths in cells, readable colours, safe fonts.
- Images: hosted, sized, with alt text, never the whole signature.
- Behaviour: short on replies, set up on every device, tested by sending.
Email signature best practices for the words
1. Use one job title, in words clients use. Bad: “Growth Ninja | Dreamer | Coffee Lover”. Good: “Head of Partnerships”. A stranger reads the title to decide how seriously to take the message, and a joke title makes that harder.
2. Give one number per purpose, in international format. Bad: “0803 555 0177”. Good: “+234 803 555 0177”. A local-format number cannot be dialled from another country, and a signature gets forwarded to people in other countries more often than you expect.
3. Make link text say what the link does. Bad: a pasted address ending in a string of tracking codes. Good: “Book a 20-minute call”. Short link text also keeps the character count down, which matters in Gmail, where Google says a signature can hold up to 10,000 characters.
4. Stop at four to seven lines. Bad: twelve lines, four numbers, two quotes. Good: name, title, company, one number, one link. This one is our advice, not a limit, but a signature taller than the message it follows makes short replies look odd.
Email signature best practices for the build
5. Lay it out in tables, not floats. Bad: two columns made with floated divs. Good: a table with two cells. Microsoft’s archived reference on the Word-based engine behind Outlook for Windows lists float and position as unsupported CSS (Word HTML and CSS rendering in Outlook). That page describes Outlook 2007 and is archived, so treat it as a cautious guide and test in the version you care about.
6. Put width, height and padding on table cells and images. Bad: padding on a span. Good: padding on the td. The same Microsoft page gives span only a small set of properties (no width or padding), while table, td and img support width, height and padding. Newer Outlook apps may differ, but the table-cell habit is safe everywhere.
7. Check the colour contrast of small text. Bad: pale grey (#aaaaaa) on white, a contrast ratio of 2.3 to 1 by the WCAG formula. Good: a mid-grey such as #4a5568 on white, about 7.5 to 1. The W3C’s contrast criterion asks for at least 4.5 to 1 for ordinary text. It is a web accessibility standard, not a mail rule, but the readers are people too.
8. Pick fonts the reader’s device has. Bad: a single brand font that is not installed on most machines. Good: a stack such as Arial, Helvetica, sans-serif. This is advice from practice, not a vendor rule: when a font is missing, the app substitutes one, and your spacing shifts with it.
Email signature best practices for images
9. Host the logo at a web address. Bad: an image pasted straight into the signature box. Good: an image inserted by web address. Gmail’s help for administrators lists three ways to add an image (a web address, My Drive, or an upload) and says Drive images must be shared publicly or they will not appear in the signature. Microsoft also warns that VML tags in a signature can make some elements appear as attachments instead of inline images.
10. Size the logo in the code, and save it larger. Bad: a 1,600-pixel file squeezed down by the app. Good: a file at twice the display width with the displayed width set. Our size guide has the numbers. This is a rule of thumb for sharp screens, not a limit.
11. Write alt text on every image. Bad: no alt text, so a blocked logo is a blank box. Good: alt text with the company name. Microsoft says classic Outlook is set by default to block automatic picture downloads (Microsoft Support), and the W3C’s text alternatives criterion says non-text content needs an equivalent text alternative.
12. Never make the whole signature one picture. Bad: a single image of your name and details. Good: real text, with the logo as a small image beside it. Plain text cannot show pictures at all, according to Microsoft’s page on message formats, and a blocked picture leaves the reader with nothing. The same page says Rich Text messages sent outside your organization are converted to HTML, which is a reminder that the message the reader gets is not always the one you wrote.
Email signature best practices for behaviour
13. Use a shorter version on replies. Bad: the full block under every message in a ten-message thread. Good: the full one on new messages, and name, title and number on replies. Both apps support this. In Gmail you set a default for new emails and another for replies, and in new Outlook, checkboxes choose new messages and replies and forwards.
14. Set it up everywhere you send from. Bad: a signature on the desktop and none on the phone. Good: a version on each device. Microsoft says signatures in classic Outlook are stored on the device where they were created and may not be available on another. Gmail’s “Send mail as” feature lets you set a different signature for each address.
15. Test by sending it to yourself. Bad: judging the signature from the editing box. Good: send a real message and open it on a phone and in a second app. Microsoft’s page notes that classic Outlook does not add a new signature to the message you opened while creating it, so a test needs a fresh message.
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A ribbon layout that follows the rules above: text for the essentials, one number, one link, a small logo. The company and person are made up.
Keeping the rules alive in a team
Fifteen rules are easy for one person and hard for fifty. People paste over the logo, shrink the font, or add a quote. The fix is to stop asking each person to follow the rules and to build them into one shared design instead. With emailfooter the company admin sets the layout, logo, colours and legal line, and each employee edits only their own details. Employees still install the result in their mail app by following the steps shown. emailfooter does not push signatures into mailboxes. The complete guide compares the approaches.
Frequently asked questions
What are the best practices for an email signature?
Keep it short, use text for the essentials, host and size the images with alt text, lay it out in tables, and test it by sending a message to yourself.
What are the email signature do’s and don’ts?
Do use one title, one number per purpose and a small logo. Don’t use quotes, long disclaimers, animated images or a picture of text in place of real text.
How many characters can a Gmail signature have?
Google’s help page says up to 10,000 characters, and that images count toward it.
Should I use the same email signature on replies?
A shorter one is usually better on replies. Gmail and Outlook both let you set a different default for new messages and for replies.
How often should I review my email signature?
Whenever a title, number, address or brand colour changes, and at least twice a year. Old signatures do the most harm in forwarded messages.
Keep reading
- Email signature: what it is, what to put in it and how to set it up: Everything about the email signature: what to include, how big it should be, design rules, legal lines, examples and how to set it up in Gmail and Outlook.
- 10 email signature mistakes that make a company look careless: Ten email signature mistakes, each shown as a before and after with a one-line fix, from image-only signatures to broken links and a title that is out of date.
- Email signature etiquette: what is polite, what is noise: Email signature etiquette in one table for new emails, replies, long threads and internal mail, plus nine habits that waste the reader’s attention.
- Email signature size: width, image size and character limits: What is the best email signature size? Recommended width, logo dimensions, image file weight and the character limits in Gmail, so your signature looks right.
Make every signature in your company match
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