Hiya...Just found out you posted identical questions - as a heads up, please don't do this unless at least week has elapsed with no responses. It can mean different people repeating information which not only wastes time, it can mean the continuity of conversation gets lost.

However, I'm not sure whether you repeated the question because you posted one into the wrong place eg: Thunderbird V Thunderbird Android  ?

If there is a similarity on icon use and you are talking about the 'Envelope icon with dot' on the top area then it may be performing the same - show or sort by unread.

I've been trying to locate some Help Articles but they are somewhat limited.

In Thunderbird generally In 'Quick Filter' toolbar The icon which is 'Envelope with a dot in top left corner' is 'Show Only Unread Messages' filter option. You would select it to only show unread emails and delect to show all emails.

If using 'Table View' you will see column headers. One column header shows an 'Envelope with a dot in top left corner' and if you click on it - it means 'Sort by Unread' and each email will have a green dot in that column if status is 'Unread'.

Hi Toad-Hall, I moved my question to Android, as suggested by someone. It's still there in the first forum because I haven't found out how to delete it. I'm guessing your reply is for TB on the PC. In the Android version, if you open a message, there is an envelope with a dot above the message next to the trash icon.