For some emails, yellow envelope started appearing in email icons in Outlook. What does it mean?

Dear mik256

Thanks for choosing Microsoft Community.

Based on your description, I know the scenario you met. The yellow envelope icon in Outlook typically indicates that the email message has not been read yet. However, since you mentioned that opening and reading the email does not make the icon disappear, it could be a bug or a glitch in the software. For this, please be kindly to try the suggestions bellowing and check if these can make any difference.

1. Repair Office Application: Repair your office application: You can refer to  Repair an Office application (microsoft.com) and then check the result.
2. Create a new profile according to Create an Outlook profile - Microsoft Support.
3. Use SaRa Tool to fix your outlook issue: You can get more detailed information from About the Microsoft Support and Recovery Assistant.
4. Un-install outlook and re-install it.

Hope the suggestions above can help you. If the issue persists, please be kindly to provide me the screenshot about your Outlook version. I will continue to help you based on the information you provide. Your understanding is highly appreciated.

Thanks for your precious time. Have a nice day.

Best Regards,

Katherine

If you can wait this annoyance out, it seems Microsoft does intend to fix it.

You can follow that thread here: Released: March 2024 Exchange Server Security Updates - Microsoft Community Hub

While this seems technically correct, the envelope icon appears to simply be replaced with a "reply" arrow icon:

From what I gather here, Released: March 2024 Exchange Server Security Updates - Microsoft Community Hub, it should be fixed when Microsoft fixed the March 2024 Security Updates for Exchange.

Problem seems to be the message property PR_ICON_INDEX, which is value 0 for affected mails with yellow icon. New mails should be -1 though. After reading, the value will be deleted from outlook, but only if it was -1 previously.