Again in 2019, Microsoft introduced a giant change to its record of blocked file varieties for attachments. On the time, Microsoft said that it was doing so to enhance safety by including “file extensions to the BlockedFileTypes property of current OwaMailboxPolicy objects.” The tech large deems such file varieties as not safe for attachments and is an efficient technique to shield clients from probably malicious assaults from risk actors.

Over time the corporate has expanded the block record for Outlook for the Net and likewise the New Outlook for Home windows app. In a brand new message by way of the Microsoft 365 Admin Heart portal, the corporate has introduced that two extra such file varieties might be added. Nevertheless, the tech large feels this could not have an effect on most customers, as these “newly blocked file varieties are hardly ever used.” It writes:

“As a part of our ongoing efforts to boost safety in Outlook Net and the New Outlook for Home windows, we’re updating the default record of blocked file varieties in OwaMailboxPolicy. Beginning in early July 2025, the next file varieties might be added to the BlockedFileTypes record:

• .library-ms
• .search-ms”

For admins, Microsoft says that no motion is required if their respective organisations don’t depend on the aforementioned file attachments. Nevertheless, if they’re nonetheless in use, then admins can “add them to the AllowedFileTypes property of your customers’ OwaMailboxPolicy objects earlier than the rollout.” Talking of which, that is set as a “main change” with the rollout anticipated to start out in early July 2025.

You will discover data on how to try this within the official documentation on Microsoft’s web site right here.

For these questioning, the next file varieties are allowed by default: “.avi, .bmp, .doc, .docm, .docx, .gif, .jpg, .mp3, .one, .pdf, .png, .ppsm, .ppsx, .ppt, .pptm, .pptx, .pub, .rpmsg, .rtf, .tif, .tiff, .txt, .vsd, .wav, .wma, .wmv, .xls, .xlsb, .xlsm, .xlsx, .zip”

You will discover the record of blocked file varieties right here on this Microsoft help article on the corporate’s official web site. In case you are a system admin, you possibly can view the message on the Microsoft 365 Admin Heart beneath ID MC1090702.