If the user does not exist in Xink and the add-in is installed, their own created signature will remain. However, they will receive an error below. The user can ignore the error and can still use his own signature.
Our suggestion is to create a group for your Xink users and select the option, "specific users/group" or you can change your deployment method to “Available” but It requires user interaction.
If you are only getting this error on Android, this means your UPN is different from your SMTP which will not work due to a Microsoft framework that runs behind it. Please see the same info in the Manifest Deployment Guide.
The workaround is to create a copy of your user with an email address that matches your UPN or configure a fully-server-side setup to apply the signature once the email is sent. Click here to know how to configure server-side.
