Using shared mailbox on mobile device with Exchange 2019 On-premise.

Hello!

Maybe somebody can help me with my strange situation.

Deployment:

1. On-premises 2019 Exchange server (15.02.1544.011) installed on Windows Server 2019 fully updated (and restarted) today.
2. Regular User mailbox called user
3. Shared mailbox called shared_mailbox
4. Permission for user to user shared_mailbox :
   1. Add-MailboxPermission shared_mailbox -User user -AccessRights FullAccess -AutoMapping $false
   2. Add-ADPermission -Identity shared_mailbox -User user -AccessRights ExtendedRight -ExtendedRights "Send As"

Problem:

Everything works fine with desktop outlook client and OWA. User can send message from itself and send as shared_mailbox.

User can add and use without any error his own mailbox from outlook for iOS.

But user cant send message from shared_mailbox using outlook for iOS.

I can't follow this manual, because there is no option "Add a shared mailbox" in outlook app.

https://support.microsoft.com/en-us/office/add-a-shared-mailbox-to-outlook-mobile-f866242c-81b2-472e-8776-6c49c5473c9f

The error text:

We couldn't deliver your message.
Original message details
Created date: 7/2/2024 10:31:50 AM
Sender address: shared_mailbox@contoso.com
Recipient addresses: recipient@fabrikam.com
Subject: Test


Technical details
EasSendFailedPermanentException: An EAS Send command failed: The EAS command failed with Status MailSubmissionFailed, Code ='120' and HttpStatus OK. --> The EAS command failed with Status MailSubmissionFailed, Code ='120' and HttpStatus OK.
Failure code: a056

And error message exist only in mobile client, it does not sync to server (and doesn't appear in desktop outlook). So, I suggest, the message doesn't even uploads to server.

Any ideas?

Thanks in advance.