[German]I got reports from German readers who use Office version 2505 in a Click-2-Run version (e.g. Office 365). They are losing mails in Outlook 365 version 2505 when moving them to subfolders when cached mode is activated.
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German blog reader has now reported on June 3, 2025, that he has come across a possible bug in Microsoft Office that could cause a lot of trouble. After I published the German edition of this blog post, several other German blog readers has confirmed the observation outlined below in Outlook classic.
Mails disappear when they are moved
The reader described the issue as: As soon as mails are moved from the inbox of a shared mailbox to a subfolder, the message does not arrive there in the target folder. David discovered this because a colleague contacted him on June 2, 2025 and pointed out the problem.
He then started Outlook 365 on his system and was also able to reproduce the behavior – although his colleagues still smiled at this statement that day. However, this changed when two of these colleagues performed an Office 365 auto-update to version 2505 on June 3, 2025. The same problem then appeared in Outlook 365 on these clients.
Nothing on the network yet – tests unsuccessful
The reader wrote that he had not yet been able to find anything similar to this error pattern online. But the error is reproducible and could be a serious problem, the reader notes.
David then carried out multiple tests with and without the cache switched on, and also tried moving mails directly in the browser. According to the reader, this test coverage made it possible to narrow down the problem directly. On June 3, 2025, he also moved his OST files to:
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[ C:\Users\*Username*\AppData\Local\Microsoft\Outlook ]
and have recreated it also. He even went so far as to have the entire Outlook folder recreated. The error pattern does not change; if the cache is active, mails are lost when they are moved. The reader wrote that his colleague also experienced that the folder structures in the shared mailbox "flicker" or simply collapse.
The current solution to the problem only seems to remove the checkmark from the option that shared mailboxes should be included in the offline cache.
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This sounds like a problem that crops up from time to time; moving a folder into another mailbox via Outlook and the folder seems to disappear. Odds are that the folder is visible on the web, and when I've seen this problem in the wild the folder will appear eventually or you can force it by renaming the folder on the web.
We are seeing the same issue.