Microsoft announced it will expand the list of blocked attachments in Outlook Web and the new Outlook for Windows starting next month.

Microsoft announced it will expand the list of blocked attachments in Outlook Web and the new Outlook for Windows starting next month.

The company said on Monday in a Microsoft 365 Message Center update that Outlook will block .library-ms and .search-ms file types beginning in July.

"As part of our ongoing efforts to enhance security in Outlook Web and the New Outlook for Windows, we're updating the default list of blocked file types in OwaMailboxPolicy," Microsoft said. "Starting in early July 2025, the [.library-ms and .search-ms] file types will be added to the BlockedFileTypes list."