Any version of LetMobile
You are trying to register additional user in LetMobile and as you go through the process you see the error "Mail domain is not registered"
You will see this if you are trying to register for a user with a different domain that has not been registered yet in the LetMobile Server.
To resolve this you will need to register to create a tenant for the new domain. To do this you will need to open a browser and type in https://yourletmobileservername/register.jsp and follow the steps to create a new tenant.
For example: If my LetMobile Server name is letmobile.landesk.com then I would go to: https://letmobile.landesk.com/register.jsp to create a new account