Grant a user Full access to a mailbox or entire mailbox store.
1. Run Powershell
-If you get the following error go to the end of the article to resolve the issue
Files cannot be loaded because running scripts is disabled on this system
2. Run the folling Commands
-$o365cred=get-credential
-$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $o365cred -Authentication Basic -AllowRedirection
Import-PSSession $session
-Get-Mailbox | Add-mailboxpermission -user %username%Alan@domain.com -AccessRights FullAccess
change %username% to the admin account you want to grant access
Fix Error about Execution
PS C:WINDOWSsystem32> get-executionpolicy
Restricted
PS C:WINDOWSsystem32> set-executionpolicy -executionpolicy unrestriced.