Download the Signitic plugin by clicking on the button below
Drag and drop Signitic.app in the Applications folder.
Connect via Google, Office 365 or with your secret key.
WARNING: This may cause your current signatures to be erased. Signitic will replace all signatures with your email in it.
Open Apple Mail and go to the menu: Mail > Preferences > Signatures, create a signature and put your email in it as on the screenshot below.
Back to the Signitic client, update your signature by clicking on the Update button on the bottom of your profile page.
If the signature is not updated and/or the upload is running in a vacuum, open "System Preferences" on your Mac, click on the "Security and Privacy" icon and check that in "Automation" the boxes related to Signitic are checked.
A second action must be taken on MacOS Catalina, by going to the Full Disk Access tab and adding the following 3 applications: Finder, Terminal and Signitic.