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At the moment the Dynamics 365 App for Outlook does not allow for below. These should be built into development roadmap with consideration that this capability was available through .com add in which is now being deprecated:

• Dynamics 365 App for Outlook
Invited users will not be able to use their own tenant email addresses when performing email related transactions in the host environment. Server-side synchronization of invited users’ incoming and outgoing emails are not supported as there can be complications, especially for invited users who are already syncing their emails in their own tenant.

• Invited users cannot perform email activity using their own email address. Model-driven apps in Dynamics 365 only synchronizes incoming and outgoing emails from Microsoft Exchange Online that is hosted in the same Office 365 tenant.
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