Outlook 365 Outbox: Online mode no longer possible for shared mailboxes

[German]Call for help from a blog reader struggling with Outlook 365 and shared mailboxes. In Outlook clients, online mode is no longer possible with shared mailboxes. Mails are no longer moved from the Outbox to the Sent Mail folder. The question that arises: Do any other readers have this or is the problem in the blog reader's environment.


German user Frank G. contacted me via email at end of September 2022, because he came across articles on the blog about similar issues. Frank is administrator for an enterprise environment with Outlook 365 and describes the problem he is experiencing as follows:

We have MS Exchange 2016 Std CU23, clients Outlook 365 installed locally, the own personalized accounts with cache, the shared accounts in online mode, set up separately, without automapping.

The following problem has occurred for us in the meantime with all "shared mailboxes":

For about 1-2 months now, the sent email is no longer moved from the outbox to the respective sent folder. It simply remains in the outbox, but is sent.

We have always worked on the clients with the ReGeintrag "DelegateSentItemsStyle"=dword:00000000, which also worked properly.

Of course, the administrators have to adjust various things on the Exchange server regarding the accounts. In addition Frank writes, we tried meanwhile:

Exchange accounts adjusted with

  • Set-Mailbox <konto> -MessageCopyForSentAsEnabled $true -MessageCopyForSendOnBehalfEnabled $true
  • For clients without Reg DelegateSentItemsStyle"=dword:00000000
  • Completely new profile under Outlook

But reliably it works meanwhile only in cache mode.

But what is not useful for us and we would like to get the online mode back.

The question from him was if I had read or heard anything, which I have to deny at this point. There is the blog post Microsoft 365: Shared Mailboxes not updating (Jan. 2022), but it refers to individual mailboxes. There is the support post from Microsoft updated to Sept. 13, 2022, Shared mailbox is not automatically refreshing for new email in Outlook, but it describes a slightly different bug, which is supposed to be fixed. The post here also gives some troubleshooting info, but probably won't help. Question to blog readers if there is anything known?

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