highlight emails requiring action

[GrahamSmith]

Apart from emails that can be permanently deleted, I keep all my emails, whether read or unread, in my inbox.  By default, unread emails are automatically highlighted, so I always know which ones I haven't opened and therefore may potentially need some response or action.  But as soon as I open an email to read it, or just to look at it quickly, it ceases to be highlighted, so later, when I check my emails, I have no idea which un-highlighted emails may require some action (apart from any reply I may have sent). 

I know I could edit the email's subject line to include ACTION REQ'D or similar, but this takes time and effort, and it would be far more convenient if I could just click on a button or icon or similar to indicate that this email still requires some ACTION from me regardless of the fact that it is not highlighted.  It could be a simple as inserting ACTION REQ'D? or similar at the start of  the subject line.

Please could you incorporate this or something similar into Thunderbird.

[Jon]

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