Download the Outlook plugin by clicking on the button below :
Place the Signitic.app application in the Applications folder.
Launch the application and log into your user account.
CAUTION: This may cause your current signatures to be erased.
Open Apple Mail and go to the menu: Mail > Preferences > Signatures and create a signature by putting in the signature content firstname.lastname@example.org as on the screenshot below.
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.