BleepingComputer reported on October 7 that Microsoft plans to add .msix and .msixbundle to blocked attachment types for Outlook on the web and new Outlook for Windows. Citing a Microsoft 365 Message Center notice, the report says rollout should begin in early November and reach general availability by mid-November. The notice itself requires administrator access; the reported schedule has not been independently confirmed here.
Microsoft’s public Exchange documentation explains that the blocked-file policy controls whether attachments can be viewed or saved through Outlook on the web. It also states that an allowed-file entry takes precedence over a blocked-file entry.
NAOAT analysis
The immediate organizational question is whether anyone still distributes legitimate application packages through email. A development team may send a test build to colleagues, while a help desk may forward an installer supplied by a vendor. Those workflows need an identified owner before a mail-policy change becomes a support incident.
A better preparation exercise would follow one actual package from its publisher to its intended user. Record how the recipient verifies the source, which team approves installation and where the approved copy is retained. This can reveal whether email is merely a notification channel or the organization’s unofficial software repository.
The distinction matters when an exception is requested. If the real requirement is access to a trusted release, restoring a broad attachment route may solve the wrong problem. A controlled distribution location could preserve the workflow while making ownership and version history clearer. Administrators should confirm their tenant notice and effective policies before changing settings, then give affected employees a specific supported route rather than an unexplained failure message.