shared mailbox permissions

Question

Hi All

i am using exchange 2016 hybrid environment. i have created remote shared mailbox on exchange onprem and also i have created mail enabled security group in exchange onprem.
When i try to execute the below syntax in exchange online i am getting the below error. is this not supported? I also would like to provide SendAs permissions. experts guide me.

Add-MailboxPermission -Identity sharedmailbox@Company portal .com -User mailenabledsecuritygroup@Company portal .com -AccessRights FullAccess -Automapping $false -InheritanceType All
WARNING: An unexpected error has occurred and a Watson dump is being generated: Object reference not set to an instance of an object.
Object reference not set to an instance of an object.
+ CategoryInfo : NotSpecified: (:) [Add-MailboxPermission], NullReferenceException
+ FullyQualifiedErrorId : System.NullReferenceException,Microsoft.Exchange.Management.RecipientTasks.AddMailboxPermission
+ PSComputerName : outlook.office365.com

Answer 1

@Glenn Maxwell

You could have a look about this article: Permissions in Exchange hybrid deployments

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Answer 2

You can't set the automapping for groups:

https://learn.microsoft.com/en-us/powershell/module/exchange/add-mailboxpermission?view=exchange-ps

Use this and it should work (use Exchange Online Powershell)

Add-MailboxPermission  ******@contoso.com -User ******@contoso.com -AccessRights FullAccess  

For sendas:

Add-RecipientPermission ******@contoso.com  -AccessRights SendAs -Trustee ******@contoso.com  

Answer 3

i am still getting the same error, even from GUI as well