Apple Mail (on both macOS and iOS) is designed to follow a principle called “send what you compose.” The email client determines the format of an outgoing message based on the content it detects in the compose window, not on a blanket setting.
The logic works like this:
When you compose a new message, Apple Mail evaluates whether the content in the body requires rich formatting (HTML) to be faithfully represented. If everything in the message body is plain, unformatted text, Mail concludes that plain text is sufficient and sends the message in plain text format, even if you have a beautifully designed HTML email signature attached
This is a deliberate design choice rooted in email best practices: plain text is lighter, universally readable, and less likely to be flagged as spam. Apple prioritises it unless there is an explicit reason to use HTML.
The Fix: The white bold dash trick
This is a simple, clever workaround that forces Apple Mail to treat every message as HTML, without any visible impact on your outgoing emails.
How It works
By inserting a single character — a dash (—) formatted as bold and coloured white — into your email signature, you introduce genuine HTML formatting into every message that uses that signature. Apple Mail detects the formatting and switches to HTML mode for the entire email, preserving your signature and any other formatting.
Because the character is white, it is invisible against any standard white email background. Your recipients never see it. Your email looks exactly as intended.
Step-by-Step: Adding the white bold dash to your signature
On macOS (Apple Mail)
- Open Mail and go to Mail → Settings (or Preferences on older macOS versions).
- Click the Signatures tab.
- Select the email account and signature you want to modify, or create a new one.
- Click in the signature editing area to place your cursor. Position it at the very top of the signature, before any other content.
- Type a single dash: — You can use an em dash (Option + Shift + Hyphen on a Mac keyboard) or a regular hyphen. Either works.
- Select the dash character you just typed.
- Apply bold formatting (Command + B).
- Change the text colour to white:
- Go to Format → Show Fonts (Command + T) to open the Fonts panel, then click the colour swatch, or
- Go to Format → Show Colors and select pure white (#FFFFFF).
- Click away to deselect. The dash will appear to vanish (it is white on a white background).
- Close Preferences. The change is saved automatically.
On iOS / iPadOS (Mail App)
- Apple Mail on iPhone and iPad has more limited signature editing. For a fully formatted HTML signature with this trick applied, the recommended approach is:
- Create the signature on macOS first, using the steps above, which syncs via iCloud.
- Alternatively, paste a white bold character by emailing it to yourself and copying from there.
Verifying It worked
To confirm your emails are now being sent as HTML: Send a test email to a Gmail or Outlook address you control.
*NOTE
This is a workaround, not a setting. Apple has not provided a straightforward “always send as HTML” toggle in Mail. This trick has been in use by Mac power users and email designers for many years and remains the most reliable method available.