Outlook will strip attachments from some forwarded emails once you've applied a security update from this month's Patch Tuesday, Microsoft has admitted.
Once the buggy patch, released January 9, is installed, Outlook 2016 will drop attachments from forwarded plain-text messages. This affects the Microsoft Installer (MSI) version of Outlook, but not the click-to-run versions (like those in Office and Office 365). The patch is supposed to prevent dodgy Office documents from executing malicious code when opened.
Microsoft said users can check whether their version of Outlook is the affected MSI app by looking in the "Update Options" screen. Click-to-run builds have an "Office Updates" option while MSI versions do not.
Alternatively, you could just check by trying to forward a plain-text email with an attachment.
Shortly after the security patch was released, IT admins began reporting that file attachments were getting cut out of messages when forwarded to others. Users also noted that the attachments were dropped in both the sent email and the copy saved to the sent folder.
Microsoft this week released a fix to address this attachment-gobbling bug, but says the update won't be rolled out to all users until next month's Patch Tuesday release on February 13. Users and admins who don't want to wait until the middle of next month can manually install KB4011123.
Even if it does have a tendency to mess up Outlook, the January security update is considered an important one for Office. Among the 56 vulnerabilities addressed in the Microsoft update was a remote code execution flaw in Office that was already being actively targeted in the wild. ®