"to send as" options in security groups from Active Directory

[Frdrick_Lefebvre]

Good morning everybody.

I can't modify "to send as" members options in Exchange Administration Center for security groups.

This security groups was created in Active Directory. Members are presents in EAC as AD.

I have read the Microsoft's documentation : Allow members to send as or send on behalf of a group | Microsoft Learn and Manage mail-enabled security groups in Exchange Online | Microsoft Learn ; but options are not visible in EAC. I think that's not right problem. I can do this for SharedMailbox.

I have contact Microsoft 365 support, but they said this options ("to send as") is absent in EAC cause this object was created and synchronised from AD. They don't know where I can modify members allow "to send as". Some members of this security groups can send as. But we add new members some days ago. This last one they can't.

How do I to add new members allow to send as for security groups created in Active Directory ?

Best Regards, 

[#2]

@Frdrick_Lefebvre 

Proceed by adding members to security groups in Active Directory Server.

[#3]

I did this.
Old members can send as.
But new members can't. It's not Outlook problem. We select the right email adress in From. They received an error that they don't have permission.

[#4]

Try adding a new member address by checking the msExchSendAsAddresses value of the group properties in ADSI Edit!

[#5]

Ok.
The msExchSendAsAddresses value was empty. So it can't be the right options because I have some old users that can send as this security group.
But I did what you said. I'v added one member in msExchSendAsAddresses. I'd waiting M365 synchronisation. I'v tested send email. But error again. I'v found another how-to in Internet (https://tchekbo.wordpress.com/2021/08/09/send-as-or-send-on-behalf-for-active-directory-distribution...) so I add this member in security and allow "total control". I'd wait another synchronisation. Test again. Error again.

[#6]

Do you have an on-premise Exchange Server?
If so, set it up in the on-premise management center!

[#7]

No. There is only cloud (via Microsoft 365) Exchange Server.
Regards.

[#8]

@Frdrick_Lefebvre 

Am I right in thinking that SendAs is working for some of the members of the Security group, yet for new members added they get "permission denied"?

Are your users running/using Outlook in cached mode, if so, is their Offline Address Book (OAB) upto date?

When entering the address to "SendAs" is the entry being selected from the OAB or being "free-typed"? Try selecting clearing any existing troublesome entries from the "FROM" list/drop down and then selecting the entry from the OAB

[#9]

Hello.

Yes. We are in cached mode in Outlook. But this email adresse is a old address. So they don't have Address Book issue.
Select from OAB or free-typed address in the "SendAs" form is indifferent. I have a shared mailbox that I use in SendAs and I add it manuelly to SendAs in "free-typed mode". There is no right problem to "SendAs" from this shared mailbox.
Members of security group received email send to fhis group. But for recent members adds to this group, they can't SendAs. I know that's a right different. In the past this rights was adding by old Exchange center. But in the new, I can't find this right option.

[#10]

@Frdrick_Lefebvre 

Did you find the solution?

[#11]

Connect to Exchange Online with PowerShell and use the cmdlet : Add-RecipientPermission "GroupName" -Trustee "MailboxName" -AccessRights SendAs
Check with : Get-RecipientPermission "GroupName"

[#12]

Thank you!! That works!!