When I try to delete a user from Active Directory, It shows me the confirmation dialog box
Object contails other objects. Are you sure you want to delete object and all of the objects it contains?
If you cancel the running deletion, the objects delete thus far will not be recovered.
WARNING: if you select Use Delecte Subtree serve control checkbox, all objects within the subtree, including all delete-protected objects, will be deleted, and the deletion connaot be canceled.
Do not worry, this is normally from Exchange attributes have attached to that user account. please follow this guide you will do it.
Step 1: view the Sub objects
Open Active Directory Users and Computers -> Click view and tick “Users, Contacts, Groups, and Computers as containers”.
Then you will see a triangle symbol next to the user account. Click on it to expand the contents and view the objects. Here we can see some old Active sync device information leftover from an old Exchange server installation.
You can now delete the user and all child object safely.