Policies - RTF Attachment Blocking Update - Jan 2026

Service Update

Availability	January 8th, 2026
Product(s)	Email Security Cloud Gateway, (CG)
Who's affected	Administrators and End Users

Overview

Mimecast is pleased to announce that we have released an update to our content analysis engine that improves detection of embedded files within Rich Text Format (RTF) attachments. Previously RTF files containing embedded Windows Metafile (WMF) images were not consistently identified.

The update now correctly identifies these embedded files, ensuring Attachment Management policies apply as intended.

What's changing

• RTF files containing embedded WMF images now trigger this protection.
• If your Attachment Management policies block WMF files (such as default "Block Dangerous File Types' policy), RTF files containing embedded WMF images will now be blocked consistently with those policies.

Recommended actions

If your organization requires RTF files with embedded WMF images for business operations, create a custom Attachment Management policy to support these use cases and ensure required files are delivered.

Review your Attachment Management policies if users report blocked RTF attachments.

For questions about this update, or assistance configuring Attachment Management policies, log a support request via Mimecast Support.

See Also...

• Policies - Configuring Attachment Management Definitions