Setting up HTML signatures in Apple Mail

Setting up HTML signatures in Apple Mail on macOS involves several steps—some of which can be tricky—so we’ve put together this guide to walk you through the process.

Keep in mind, this only works on macOS as iPhones and iPads don’t support custom HTML email signatures.

Step 1

Open the Mail app on your Mac and navigate to the Settings… pane.

Step 2

If you already have a signature applied to your account and just want to update it with a new HTML version, you can skip ahead to Step 5. Just make a note of your current signature text—you’ll need it later to identify the correct signature file.

In the Settings pane, there are a few things we need to do:

1. Click on the Signatures tab.
2. Ensure that All Signatures is selected in the list on the left-hand side.
3. Click on the plus (+) button at the bottom of the list.

Step 3

Great, you’ve just added a new signature which will have a name similar to Signature #1. You can either leave this name as is, or enter something custom such as My Company – Support by double-clicking on the signature in the list.

Your Signatures pane should now look similar to this:

Step 4

Next, we’ll need to set this new signature as the default signature for your email account:

1. Ensure that All Signatures is selected in the list on the left-hand side, then drag the signature from the second list onto the email account in the left-hand list.
2. Click on the email account you just dropped the signature onto in the left-hand list.
3. At the bottom of the pane in the Choose Signature dropdown, select the newly created signature from the list.

Step 5

We’re done in the Mail app for now, so quit it by selecting Quit Mail from the Mail menu item in the menu bar at the top of your screen.

Note: Closing the Mail window isn’t the same as quitting it. You’ll need to actually quit the Mail app before continuing as we’re about to make changes to some internal files that the Mail app uses.

Click on your desktop, or the Finder app all the way on the left-hand side of your Dock at the bottom of the screen.

Now, click on the Go menu item in the menu bar at the top of your screen, then choose Go to folder….

Step 6

In the panel that opens, you’ll need to type in the path ~/Library/Mail and then press Enter on your keyboard.

Hint: You can either copy and paste the path from above, or type it in. You can type the tilde (~) character by holding either Shift key and pressing the key immediately on the right of the left-hand Shift key if you have a British English Magic Keyboard from Apple.

Step 7

A Finder window will have opened which shows you the contents of the ~/Library/Mail folder.

You might see a few different folders in here starting with the letter V followed by a number. In our example, we only have one folder—V10—but you may others like V8 or even higher numbers.

Open the folder with the highest number. So, if you have multiple folders such as V8 and V10, open the V10 one.

Step 8

Open the MailData folder.

Step 9

Open the Signatures folder.

Step 10

This folder contains several files, but we’re only interested in those with the .mailsignature extension.

In our case, there’s only one signature, so there’s just a single .mailsignature file—making it easy to identify the one we need to edit.

If you have multiple .mailsignature files, you’ll need to figure out which one corresponds to the signature you want to update. There are a couple of ways to do this:

• Check the modification dates: If you’ve recently added or updated the signature, look for the most recently modified file.
• Open and inspect the contents: If the timestamps aren’t helpful, open each file and check the contents to find the one that matches your signature (we’ll show you how in the next step).

Step 11

Right-click on the appropriate file from the previous step, then move your cursor over the Open With item, and then click on TextEdit.

Step 12

The TextEdit app will have opened with the contents of the file. We need to replace everything inside the body element with your new HTML email signature (the highlighted text in the screenshot below).

Step 13

Now, open your new signature file the same way you did in the previous step. In the screenshot below, the .mailsignature file to be updated is on the left, and the new signature is on the right.

Copy the entire HTML email signature from the new file and paste it into the appropriate section of the .mailsignature file.

Be sure to only replace the content between the opening <body …> and closing </body> tags—don’t overwrite the entire file. The screenshot in the previous step highlights the section to replace, and the one below shows the updated file with the new content in place.

Step 14

You can now save and close those two files. We just need to make one more change to the .mailsignature file, then we’re done.

Right-click on the .mailsignature file and choose Get Info from the menu.

Step 15

In the panel that opens, you’ll need to check the box with the label Locked to prevent the file from being reverted back to the previous version by the Mail app.

Step 16

If you re-open the Mail app and head back into the Settings… > Signatures panel, you should now see that your signature shows the new HTML version.

If your signature has any images they won’t show here in the preview, but they will when you draft a new email.

Step 17

Finally, we’ll draft an email to check the signature is working properly.