Microsoft Outlook to block MSIX attachments starting November
Summary
Microsoft is expanding its list of blocked file types in Outlook to include MSIX and MSIXBUNDLE attachments. This change will take effect in Outlook Web and the new Outlook Windows client starting in November. The move aims to enhance security by preventing the delivery of potentially malicious attachment types.
IFF Assessment
Blocking potentially malicious file types in email clients is a defensive measure that helps protect users from malware and other threats.
Defender Context
This is a proactive security enhancement by Microsoft to mitigate risks associated with email attachments. Defenders should be aware of this change and understand that .msix and .msixbundle files will no longer be deliverable via Outlook, which might impact legitimate use cases but broadly improves the security posture against novel attack vectors.