I am posting this to help any of you who are looking to be proactive in your approach to migrate into Office 365 / Exchange Online Services.
After migrating mailboxes info Office 365, you will noticed that under your recipient’s mailbox delegation all previous access levels have been removed. In fact they never came over with the migration in the first place.
But Why?
Because during the copy of the user account and mailbox data this info is not recorded as the migration tools are not designed to copy such info (at this time) “quoting Microsoft support on this one”
Right now I am in search of a method to script out my users and then import that via power-shell. I will post / share this as soon as I have a working solution.
This post is just to inform any of you searching this out that you may also face this same issue.
IMHO
In my humble opinion as a professional who has been working in Office 365 / Exchange Online – You are better off configuring a Hybrid migration path over the all in one cut-over-method. While the Hybrid may take some extra learning and understanding; its the path that will ensure your data is migrated with all attributes.
Another example of things not working properly in a cut-over migration: Office 365: Convert Mailbox to Shared Mailbox after Cutover Migration
Again note: that not all permissions are preserved when mailboxes are moved to Office 365 using a cutover migration. For example Send As permissions on mailboxes will be lost and administrators will need to reconfigure this once users are moved across into the cloud.