Hi @Attya, Mohamed ,
Thanks for your post!
Preventing oversharing in Outlook requires the AIP Premium P2 plan.
This is documented in the feature comparison list. https://learn.microsoft.com/en-us/office365/servicedescriptions/azure-information-protection#feature-availability
You can assign licenses per user so you can have mixed licenses or add the AIP plan 2 by itself, so you shouldn't need the full E5 plan for this. As a sidenote, if you wanted to keep users in the same repository, using the AIP scanner in "discover" mode would require just the P1 license, but using the AIP scanner to apply classification, labeling, or protection would require the P2 license.
(See pricing details here.)
That said, feel free to reach out to your licensing representative of choice to get more details about this. It's free to have a call with Azure billing. https://azure.microsoft.com/en-us/support/create-ticket/
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