try turning off your other devices and see if the mail is still marked read... IIRC the google apps for IOS mark the mail read.

I uninstalled all of my Gmail apps on iOS and ran only Thunderbird on Windows 10 and same result. One by one my messages are being marked as read as they arrive. The change seems to be in Thunderbird. It used to be that the focus in messages remained on the message being read. Now when a message arrives and the focus changes to that new message and then, after one second, the message is marked as read even though I wasn't around to read it. This occurs even in safe mode, so it is not an add-in causing this behavior.

Thunderbird has a bug where arriving messages get the focus and are then marked as read.

Did you turn off the other devices though?

The next step is see if it is an add-on causing issues.

Restart Thunderbird with add-ons disabled (Thunderbird Safe Mode). On the Help menu, click on "Restart with Add-ons Disabled". If Thunderbird works like normal, there is an Add-on or Theme interfering with normal operations. You will need to re-enable add-ons one at a time until you locate the offender.

Matt,

I appreciate your follow up, but I don't think you are fully reading my posts. In my previous post I state that I closed all other apps accessing Gmail and ran Thunderbird in safe mode, getting the same result. Thunderbird shift the focus to incoming messages, moving the new message into the reading pane and then, one second later marking the message as read. I have watched this happen. Thunderbird used to not behave this way.

If the message in in the reading pane, then it is being read. It's appearance there should mark it read. So perhaps you are right. I have no idea what it is you are complaining about.

I will copy the relevant points from my original post:

• any new imap message delivered to Thunderbird immediately becomes the focus, opening the message in the reading pane
• because the new message opens in the reading pane, my setting to mark a message as read kicks in and marks the message as read even though I was not present to view the message
• this is a recent change in behavior for Thunderbird, previously, new messages delivered to my inbox would not open in the reading pane until I manually clicked on the message

The expected behavior is that new messages do not open in the reading pane until clicked. The current behavior is that new messages are opening in the reading pane on delivery, even in safe mode and even when no other app is open to access the imap account. If I close Thunderbird and access the imap account through a web browser or gmail app the messages remain marked as unread until I open them.