The new mail icon lingers after opening all mail, until UI reload or logout.

Addon Version: v10.0.10

Any additional information?

Upon writing this, I noticed opening and closing the mailbox several times caused the icon to disappear.

I have also been encountering this, at least since DF launched. I can't recall it happening before.

I think I can confirm that it's an addon conflict. At least for me, it happens when Postal and SexyMap are both active.

• When Postal is active without SexyMap, the default minimap mail icon gets cleared without issues.
• When SexyMap is active without Postal, the SexyMap mail icon gets cleared without issues.
• When both Postal and SexyMap are enabled, the mail icon does not disappear until UI reload.

This will be a conflict with another one of your addons. Disable them all except SexyMap then gradually re-enable them until you find the culprit. Please post which addon was at fault for future users browsing these issues.