Open your HTML email signature file in your web browser.
Press Cmd + A to select the entire email signature, then press Cmd + C to copy it.
IMPORTANT: Do not use your mouse to select the area, only use Cmd + A as you may miss out on grabbing some of the code.
Open Airmail and from the menu bar select Airmail then Preferences. Select the Signatures tab at the top of the window.
Now that you're in Preferences, you should have a new window open and by default be on the Accounts tab. To the far right of your listed email account you will see a small settings cog icon, click this.
A new window will open up and you will see a few new tabs across the top, select the Signature tab. Select your email account, then click the + icon to enter a name for your signature.
Create professional email signatures that make a lasting impression. Easy to customize, always looks perfect across all email clients.
Airmail Email SignaturesClick inside the blank text box below and press Cmd + V to paste your copied email signature. Click Save.
Your email signature is now installed in Airmail for macOS and will insert when composing an email.