Apple Mail HTML email signature installation guide

This guide will help you install an HTML email signature properly in Apple Mail. Ensure you follow each step carefully.

Step 1 — Create your signature

Create your email signature in

Step 2 — Add a new blank signature in Apple Mail

Navigate to the Preferences panel in Apple Mail and follow these steps:

  1. Click on your chosen email account in the first column
  2. Add a new signature by clicking the ‘+’ symbol below the second column
  3. Name the signature ‘ signature
  4. Select the signature with Choose Signature at the bottom

Do not worry about editing the content of the signature (third column) as we will be replacing this with our own.

Step 3 — Close Apple Mail

Quit the Apple Mail app now by pressing Command(⌘)+Q or going to File > Quit.
Don’t overlook this as it is important for future steps.

Step 4 — Navigate to the signature folder

Apple Mail saves this signature to a file on your computer; this is a little hidden but can be found using a short process described below.

Open Finder and click on ‘Go > Go to Folder…’

If you are using macOS Monterey you will be able to paste in this location and it should navigate you automatically to the correct folder on your computer:


Optional (if the above location doesn’t work)

If this doesn’t work it might be that you are using a different version of the operating system. This doesn’t change too much but you will have to manually find the correct folder. You do this by opening your Library:

You’ll be presented by a large set of folders but be careful not to move, edit or delete anything here as this could break parts of your system.

  • Navigate to the Mail folder
  • Sort the folder by Date Modified so that the latest folder is at the top
  • Open the highest V folder in this directory. This could be named V6, V7, V8, V9 or similar
  • Now navigate through MailData > Signatures

Step 5 — Open signature file

There will be multiple files in this folder but you only want to focus on the files ending with .mailsignature.
You need to open the newest .mailsignature file created;
if you sort by ‘Date Modified’ you should be able to easily identity the correct one.

Your file name should look something like this:

Do not edit any files with a .plist extension.

Right click the file and select ‘Open With’ and choose

If this doesn’t appear by default, you’ll have to click ‘Other’ and choose it in your Applications directory. You can choose another preferred text editor here as long as it doesn’t leave any formatting behind. Do not try to use Microsoft Word or anything similar.

Once opened, your file should look something like this:

Step 6 — Replace signature file content

  • Copy the Signature code code by clicking the yellow ‘Copy HTML’ button:

Once you have the HTML code copied, head back to TextEdit where you should have your blank signature open.

Select everything between and including the <body></body> tags, leaving the header metadata intact:

  • Now, paste your new HTML code in place of this. Your file should now look similar to this:

Once this is complete, save and close the file.

Step 7 — Lock file

Once saved and closed, right click the file again and select ‘Get Info’. A pop-up panel should appear.

Please click on the ‘Locked’ checkbox and then close this panel. This will stop Apple Mail corrupting any of the new custom HTML.

Your signature is now installed!

After locking your email signature, reopen Apple Mail and your new signature should be installed when you start composing a new email!

Any further questions?

If you’re still having issues using Mirosign or we haven’t answered your question here, please get in touch and we can help you in person.

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