Here is a simple guide to help you insert you new custom HTML signature into Apple Mail.
Step 1: Create a new signature
Let’s go to Mail > Preferences > Signatures and click “+” button. Set e.g. “My Signature” name to your signature and add just your name (on the right) to your new email signature. Our sample email signature now looks like this:
At this point, we need to Close Preferences and Quit the Mail application.
Step 2: Find your mail signature file
Now we have to find your new signature file hidden in your Library folder. Open the Finder, click on the Go menu, and hold the Alt/Option key down. You will see the “Library” folder. Choose that Library folder and navigate to the following folder:
You should easily recognise your signature file by the Date Modified that was created Today:
Step 3: Edit HTML signature in Apple mail
Right click on the signature file. Open with > Other… and choose TextEdit application. Take a deep breath and don’t worry. You don’t need to understand this “Gibberish”. I will guide you through it step-by-step.
Your signature file will open in TextEdit and should look similar to mine:
Step 4: Replace the signature body code
Replace the the signature code, (starting on the line #7 with with “<body”), with the HTML code I have sent you.
Step 5: Save and lock mail signature file
When you are finished, Save the mail signature file (File > Save). Close TextEdit. Right Click on the file and the choose “Get Info” and click on the “Locked” checkbox (otherwise, Apple mail will destroy everything you‘ve done). Close the “Get Info” window and you’re done!