How to flag a single message in a thread? When I select a thread and click the flag button as shown in official guide, it flags all the messages in the thread. This is suboptimal when the thread is long and contains many messages. How can I flag one single message in a thread?
Select the thread.
Scroll to the message.
Hover over the space above the title. The cursor should show “grab”:


Double click, and the message will be shown in a pop-up window.
In toolbar of the pop-up window, there is a “flag” button, which will only flag this message.