Microsoft will soon be blocking an additional 38 file extensions from being downloaded as attachments in Outlook on the Web in order to protect users from malicious files. These additional extensions includes files used by Java, Python, and various vulnerabilities. These extensions are being blocked as they can be used by attackers to install malware, exploit vulnerabilities, or perform other unwanted behavior in Windows when executed. Administrators can manage the “BlockedFileTypes”” list by adding and removing extensions from it. Microsoft is cognizant that the existing list and the upcoming changes may not work well for organizations that commonly send these types of file attachments.”
Source: https://www.bleepingcomputer.com/news/microsoft/outlook-on-the-web-to-block-file-extensions-for-powershell-python-and-more/