Download or save your HTML email signature file to your computer, then open it in your Safari web browser.
With the email signature open in your Safar browser, press Cmd + A to highlight the signature, then press Cmd + C to copy the signature.
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.
Login to your Zoho Mail account and click the Settings icon at the top right of your screen.
From the left sidebar, scroll to the bottom and select Signature. Click the + icon in the next column to create a new email signature.
Enter a name for your email signature, then click inside the text field below and hit Cmd + V to paste your copied email signature. Click Save or Update at the bottom of the window.
Compose a new email and you'll see your email signature now automatically inserts within Zoho from your Safari browser.