I have had this problem for many months and no new Thunderbird update solves it. I see many threads about "no new mail sound" or "no new mail notifications" but I have narrowed my problem down to a very specific set of circumstances that I have not seen addressed before. I am using Windows 7 professional and latest TBird version which is 38.6.0., and many threads mention Linux which I don't have. If there is no new recently arrived mail in the inbox (not unread mail) the sound plays and new mail icon shows up in Windows task bar just as it should. Maximizing TB will show a highlighted envelope icon in front of the mail (my theme uses envelope icons in front of each email which are yellow when they have freshly arrived in my theme "Nautopolis". Default theme uses a little yellow asterisk in front of each email instead and I have already tried changing themes to see if it solves the problem, but it does not). The theme also shows my folder tree on far left (I leave the panel open as I often move mail to local folders once read) and the account name top most, and folder name for inbox immediately below account name will be blue instead of black indicating new mail has arrived as an additional way of letting me know. If I open any of the recently arrived mail, or if I click on my account name, the yellow "fresh email" icons go gray and the blue "account name" and "inbox" folder in folder tree go back to black, plus the new mail icon in Windows taskbar disappears. Perfectly normal. Then the next email to arrive will set off the sound and taskbar notification all over again. The problem occurs if I don't "clear" the latest notification icons by clicking on my account name, or reading any of the recently arrived mail to get all the icons back to gray or black, and remove that Windows taskbar notification. I can be sitting in front of the computer doing something else and dozens of emails can come in without ever giving me any notification again. I'll maximize TBird after an hour and there are always new emails stacked up in front of the one that originally set off the notifications. I distinctly remember older versions of TBird sounding off all day to let me know I should look at another new email that just arrived, I did not have to worry about missing something important by not leaving TBird maximized in front of me all day. I have tinkered with this many times, like restarting TBird and computer and tried turning notifications off and on again in the settings, run in safe mode with no add-ons, etc. but have never found the fix. I have not tried to completely rebuild my account profile or do a clean new reinstall of TBird as I have years of email in folders and hate to go through all that trouble just to find out this may be a common bug that I can't easily fix. I don't even know what may be lurking in my profile, I go back to the old Netscape email client days and moved to TBird years ago and I remember it being quite an undertaking to preserve everything and get TBird working right with my ISP (Verizon). I know exactly how the problem relates to having to clear the notifications to get the next new mail notification, it's not like the whole system is broken, it just flakes out in this very specific way. Is this normal behavior on new versions of TBird? Maybe the code is rewritten so you get one notification only until you open your email and check your inbox? Any thoughts out there? Thanks.