Insert a clean, HTML, horizontal line into Apple Mail messages using a clever HTML signature trick — because <hr> tags get stripped by default.
Apple Mail’s composer is a Rich Text editor, not an HTML editor. It aggressively strips or mangles raw HTML like <hr> to preserve layout integrity.
But the Signature feature allows limited HTML.
By creating a blank signature, editing its underlying .mailsignature file, and locking it, you can sneak in clean HTML that renders as a full-width divider.
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Open Mail.app.
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Go to
Mail > Settings > Signatures. -
Click
+to create a new signature and name it:Divider. -
Clear all content in the signature box — including invisible line breaks.
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Drag the
Dividersignature onto one of your accounts (middle column → left column). -
With the account selected (left column), set
Divideras the default signature in the dropdown at the bottom. -
Quit Mail.app completely.
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Open Finder, then press
Cmd + Shift + G. -
Enter the following path:
~/Library/Mail/V*/MailData/Signatures
-
V*may beV9,V10, etc., depending on your macOS version. -
Look for a recently modified file ending in
.mailsignature. The filename will be a long, cryptic string.
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Right-click the
.mailsignaturefile → Open with TextEdit. -
Go to
Format > Make Plain Text(or pressShift + Cmd + T). -
Leave the metadata lines (lines 1–6) intact. Delete everything below and paste this:
<div style="border-top: 1px solid #cccccc; margin: 20px 0;"></div>
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Save the file.
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Right-click the file again → Select Get Info → Check the Locked box.
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Close both Get Info and TextEdit.
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Reopen Mail.app.
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Compose a new message.
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Place your cursor where you want a horizontal line.
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From the Signature dropdown, select
Divider.
Et voilà — you now have a clean, full-width horizontal line that you can insert anywhere in your emails, as many times as needed.
Check the included DividerExample.mailsignature for reference.
Replace the metadata with your own Mail-generated content. Only use the
<div>line below the metadata.