How to add an email signature in Apple Mail
Mail on the Mac is the most forgiving client of the seven: it understands nearly all the HTML and CSS a signature can have. That makes it easy to install in, but a poor place to test. What looks right in Apple Mail tells you nothing about Outlook or Gmail.
Installing has one trick almost everybody misses: a checkbox that, if left ticked, swaps your signature's typeface for the message's and wipes out part of the design.
Mail handles iCloud, Gmail, Microsoft Exchange and other accounts, all in the same app. The signature is assigned per account, so you can keep the company one on your work address and a simpler one on your personal address.
Steps in Mail for Mac
- 01
Copy your signature from SignatureForever with Apple Mail as the destination.
- 02
Open Mail and, in the menu bar, go to Mail › Settings (on older macOS, Mail › Preferences).
- 03
Open the Signatures tab and pick your account in the left column.
- 04
Click + to create a signature and give it a name.
- 05
Uncheck “Always match my default message font”, below the middle column.
- 06
Delete the sample text in the right column and paste your signature with Cmd+V. Close the window; Mail saves on its own.
If you have several accounts in Mail, each one needs its signature: select the other account in the left column and repeat steps 4 to 6. A signature with images hosted at a public https address looks the same from any of them.
To have the signature added automatically, choose at the bottom of the Signatures tab which one is the default for that account.
What breaks in Apple Mail and how to avoid it
Apple Mail uses the same engine as Safari, so flex, grid, background-image, border-radius and even the <style> block work. The only feature in the matrix that stays halfway is web fonts: sometimes they load, sometimes they don't. If your signature relies on a Google Fonts typeface, always set a safe fallback font.
Precisely because everything works here, this is not the place to find mistakes. Design with Outlook desktop and Gmail in mind, since they are the demanding ones, and use Apple Mail to confirm the signature keeps its colours and sizes when you paste it.
One thing that does fail in Apple Mail is dark mode. Pure black text on a transparent background disappears when the Mac is in dark mode. Use a very dark grey such as #333333, or give the signature cell a background colour.
| Feature | Apple Mail |
|---|---|
| <table> layout | Yes |
| display:flex and CSS grid | Yes |
| <style> block in the head | Yes |
| background-image in CSS | Yes |
| Images as data URI (base64) | Yes |
| border-radius | Yes |
| letter-spacing | Yes |
| text-transform:uppercase | Yes |
| Web fonts (Google Fonts) | – Partial |
| max-width and percentage widths | Yes |
| margin on <td> | Yes |
| <img> without explicit width and height | Yes |
In total: 0 unsupported, 1 partial and 11 fully supported, out of the 12 features in the matrix. Why each one fails, in the full matrix.
Common mistakes
Leaving the font checkbox ticked
With “Always match my default message font” on, Mail replaces your fonts and sizes with the email's.
Using Apple Mail as the final test
Because it shows almost everything, it hides problems Outlook and Gmail users will see. Test there too or use the checker, which tells you in seconds what each of those clients will do with your HTML.
Creating the signature on the wrong account
The signature belongs to the account selected in the left column. Make sure it's the work one before you paste.
Frequently asked questions
Why does my signature change font in Apple Mail?
Because “Always match my default message font” was left ticked. Uncheck it and paste the signature again.
If it looks right in Apple Mail, will it look right everywhere?
No. Apple Mail is the most permissive of the seven. See what changes in each one in the compatibility matrix.
Does the same signature work in iPhone Mail?
Yes, but it is installed separately: the Mac signature doesn't travel to the iPhone on its own. Follow the iPhone Mail guide.
Are you an AI agent? This is also available as an MCP server at signatureforever.com/mcp