It's a badge showing the number of new messages.

This means that you have x unread messages.

I started getting this red number since version 91.1.2 recently. Even after I have read the unread emails, the number stays, showing me there are X emails to read when there are none. Only by clicking "Get Messages" (and getting no more messages) does the red number vanish. Looks like a bug to me.

Edit the following day: This red number is useless - the number it shows seems to bear no relationship to the number of unread messages, sometimes being higher and sometimes being lower.

PeterM

Peter, You're absolutely correct! The number does not show the actual number of unread emails. Maybe it count that high. ;-) It's totally useless and should be done away with.

It works just fine for me, but like I said, it shows the count for NEW messages, not just the unread. You could always turn it off though. See https://support.mozilla.org/en-US/questions/1349811

Stans: But the red number count doesn't reduce by 1 when you read a new message, so it is not useful - it just keeps increasing as more new messages arrive. It would be useful if it worked properly. I would prefer that rather than to turn it off. What is the Config Editor?

Later: I just discovered, under "Tools|Preferences|Incoming Mails|App icon options" that I can change the "Badge app icon" from the default "Count of New Messages" to "Count of Unread Messages". I have done this and now the red number never appears at all when new messages arrive! So it's still broken. The "App icon options" box also allows the user to turn the feature off completely, so this would be a solution for Illroute66.

PeterM

Stans: But the red number count doesn't reduce by 1 when you read a new message, so it is not useful - it just keeps increasing as more new messages arrive. It would be useful if it worked properly. I would prefer that rather than to turn it off. What is the Config Editor? Later: I just discovered, under "Tools|Preferences|Incoming Mails|App icon options" that I can change the "Badge app icon" from the default "Count of New Messages" to "Count of Unread Messages". I have done this and now the red number never appears at all when new messages arrive! So it's still broken. The "App icon options" box also allows the user to turn the feature off completely, so this would be a solution for Illroute66. PeterM

I have no idea why it's not working right on your end. It behaves as expected on my end, and being a new feature, I have no idea yet how you can proceed with troubleshooting it other than suggesting you turn it off and back on.

Just received version 91.2.0 and see that it DOES work if I select "Unread Messages", but only unread messages in the Inbox for each account. Those that have been filtered into local folders are not counted. Still not useful. What we want is something in the taskbar that tells us there are messages that need attention! PeterM

The number on this icon does not even come close to the number of "unread" messages in my inbox at any given time! I get more than a hundred email items each day, and about half are correctly caught by junk processing while another 25% are routed to folders by my own filters. I ALWAYS have a large number of "unread" email. I also have rules that tag messages automatically to help me concentrate on the important emails.

I don't know what the official definition is for a "new" message. Does it become old after an hour, 4 hours, a day? I seldom receive less than a dozen "new" emails in any hour - often several dozen. So what does it mean for a message to be "NEW" ?

In any case, my number always is a single digit, yet any of the explanations I have read are not accurate for me because if any of them were correct I would need AT LEAST a 2 digit number, and sometimes 3!

UPDATE: I now note that as I was completing this entry I went back to my T-bird screen and note that the number increased from 1 to 2. And I note that there was 1 "additional" message received while I was on this screen. So is it possible that "NEW" means messages that came in since the screen was last displayed?

Further, changing to a different folder, then back to the inbox , the icon has disappeared suggesting this IS the definition of a "NEW" message.

Is there anyone who can confirm that?

But for me this is still completely useless! I always have my email sorted by date, so the "newest" messages are always at the same location on the screen.

ALSO: I have multiple accounts on my T-bird client, and have some rules that move specific messages from less used accounts to my primary account. How does T-bird account for those "new" messages? I just verified that one account has received 3 emails today that I have not seen, yet there was NO ICON presented when I switched the display to that inbox. Ditto for the trash and junk folders which are constantly getting "NEW" mail due to the junk process and my filters.

So how does anyone make sense of all this?

it DOES work if I select "Unread Messages", but only unread messages in the Inbox for each account. Those that have been filtered into local folders are not counted. Still not useful. What we want is something in the taskbar that tells us there are messages that need attention!

Agreed. It's a known issue/bug that'll hopefully be fixed. You can search at bugzilla.mozilla.org for a filed bug report or enhancement request and vote on it of one has been filed already, or file a new one if there is none. The more votes it gets the better. Until then, you can disable it since it's of no use to you in its current state.

How would T-Bird know which messages "need attention"? I get many many many emails each day and most of them "need attention", even if it is just a thank you. Others are from clients who are having problems and they are "important" so they definitely "need attention".

How can T-Bird make such a determination. I use filters to catch as many as I can, usually based on certain key words in the subject, but that is nowhere near perfect!

So what does it mean for a message to be "NEW" ?...So is it possible that "NEW" means messages that came in since the screen was last displayed?...Further, changing to a different folder, then back to the inbox , the icon has disappeared suggesting this IS the definition of a "NEW" message.

I'm not a developer for TB, so I don't have an authoritative answer, but from my own experiments, I have observed that new messages are those that were NOT on the server when Tbird last checked for them, but have since been found on the server. There is no specific duration of elapsed time for a new message. The time that matters is when Tbird last checked the server for anything new. It does this when you switch between folders of an IMAP account and when you hit the Get Messages button or basically any action that triggers a communication with the server and a check for any messages that have appeared since it last checked.

How would T-Bird know which messages "need attention"? I get many many many emails each day and most of them "need attention", even if it is just a thank you. Others are from clients who are having problems and they are "important" so they definitely "need attention". How can T-Bird make such a determination.

It can't.

Yeah, I wasn't clear enough - it was supposed to be tongue-in-cheek.

The prior poster said "What we want is something in the taskbar that tells us there are messages that need attention!"

The point of my response was that "It can't" - there is no way for T-Bird to do that. Which message "needs attention" is a personal decision. It would see that "no attention required" would be easier, but even the junk filter fails that sometimes  :-(

Yeah, I wasn't clear enough - it was supposed to be tongue-in-cheek. The prior poster said "What we want is something in the taskbar that tells us there are messages that need attention!" The point of my response was that "It can't" - there is no way for T-Bird to do that. Which message "needs attention" is a personal decision. It would see that "no attention required" would be easier, but even the junk filter fails that sometimes  :-(

Which is why I find it very handy that the folders' names in the Folder Pane get a bold font with the unread count in parentheses when they contain unread messages, including junk. If that doesn't draw enough attention to the user, I wonder what will.

When I said "needs attention", I was thinking in generic terms, not the detail. Stans point about the bold folder names with unread counts is fine, but that's not in the icon. Perhaps the red thing in the icon should show the sum of all the "unread" counts in the folder list. Or maybe all you need is a red dot (with no number) when there is ANY bold folder with an unread count at all. Then you can see immediately in the taskbar (without having to open Thunderbird) that it has SOMETHING for you that you haven't yet seen (i.e. it needs your attention!). I think the Mozilla experts can come up with something useful, but as it stands it means too many different things to too many of us users.

PeterM