Allowing any member of a dynamic group to send as from a shared mailbox

Question

We are trying to create a dynamic Security Group in an Hybrid environment, where all our the users in that group are able to send on behalf of a specific 'Shared mailbox'. We are doing this to allow the shared mailbox to be the default sending address for emails sent via power automate, which are triggered through a PowerApp. Currently, when the power automate is triggered via a PowerApp the flow fails as user triggering the app does not have the 'Send As' permission. We are looking for a method where all mail responses come from a single centralised shared mailbox SMTP address. We would like this dynamic to ensure the group only contains current users.

• Tried a dynamic distribution list but no option to send on behalf of this type of group.
• Can't manually add users to the group as too many and the group needs to be updated regularly.
• Working in a hybrid environment.

Answer 1

You may write a Powershell script where you can use the following cmdlets in the script:

• Get-DynamicDistributionGroupMember at Exchange Online: To view the calculated membership list that's stored on dynamic distribution group objects. Please note that the results from this cmdlet are updated every 24 hours.

Ref: https://learn.microsoft.com/en-us/powershell/module/exchange/get-dynamicdistributiongroupmember?view=exchange-ps

• For each member check that member has already been given access to the related shared mailbox , e.g. Get-MailboxPermission -Identity -User

• Check the results above and if it does not return any values SendAs, SendOnBehalf, FullControl etc for the queried dynamic distribution group member then provide the the member necessary rights to act on shared mailbox e.g.

Add-MailboxPermission -Identity -User AccessRights FullAccess

according to your shared mailbox settings.