User Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Win64; x64; Trident/5.0) Steps to reproduce: Normal use of Thunderbird Actual results: A "new mail" icon remains in the system tray after leaving Thunderbird. I use a number of email servers with multiple accounts and some new messages get moved around by filters. This issue may be related to filters or multiple servers/accounts. Or maybe because some messages get deleted without ever opening them. Expected results: The system tray icon should be removed upon exiting Thunderbird.

is this accomplished using an extension ? AFAIK, we don't integrate with the system tray.

I'd think the "new mail" icon could be in the system tray. It was there some time in the past.