The first time you update signatures for Apple Mail on Mojave you will get the error message below.
You get the error because the strict security model on macOS Mojave prevents the Xink app from making changes to Apple Mail. To fix it you need to grant full disk permissions to the Xink app.
- Go to System Preferences on your Mac.
- Click "Security & Privacy".
- Choose "Full Disk Access".
- Click the "+" button (if it is disabled, click the lock in the lower left corner and enter your password).
- Browse to the Xink.app file and click "Open".
- Restart the Xink app.