Can't use EAC to add remote shared mailbox to delivery management of distribution group

In a Microsoft Exchange Server 2019 or 2016 hybrid environment, you can use the Exchange admin center (EAC) to add a user mailbox to the delivery management section of a distribution group. However, you can't use the EAC to add a remote shared mailbox instead of a user mailbox. To add a remote shared mailbox as a recipient, you have to run a script in Exchange Management Shell. By using a script, you can add either one remote shared mailbox or multiple mailboxes.

Note: In the following scripts, replace <DistributionGroupName> with the name of your distribution group, and <New remote shared mailbox Identity> with the name, alias, or email address of the remote shared mailbox.

Add one remote shared mailbox

$groupname = "<DistributionGroupName>"
Set-DistributionGroup $groupname  -AcceptMessagesOnlyFrom((Get-DistributionGroup  $groupname).AcceptMessagesOnlyFrom + "<New remote shared mailbox Identity>")

Add multiple remote shared mailboxes

Each remote shared mailbox to be added must be listed in a text file that uses a separate line for each entry. In the following example, the file is named remotesharedmailboxes.txt.

$groupname = "<DistributionGroupName>"
$remotesharedmailboxes = Get-Content C:\ remotesharedmailboxes.txt
Set-DistributionGroup $groupname  -AcceptMessagesOnlyFrom((Get-DistributionGroup  $groupname).AcceptMessagesOnlyFrom + $remotesharedmailboxes)