Remove Full Delegate Permissions
Remove-MailboxPermission -Identity <janedoe@domain.com (target mailbox)> -User <janedoe@domain.com (overseer mailbox)> -AccessRights FullAccess
Prepping your Computer to connect to ExchangeOnline
Set-ExecutionPolicy RemoteSigned
Install-Module -Name ExchangeOnlineManagement
Import-Module ExchangeOnlineManagement
Connect-ExchangeOnline
Add Permissions without AutoMapping
Add-MailboxPermission -Identity <janedoe@domain.com (target mailbox)> -User <janedoe@domain.com (overseer mailbox)> -AccessRights FullAccess -AutoMapping $false