Quick filter is only showing one email but says there are 9.
I received an email last Thursday and by Sunday I wasn't able to see it my Thunderbird, I have it on other devices and tried forwarding it to myself and thunderbird acts like it downloaded a new messge but doesn't show up in my inbox. When I do a quick filter of the subject, it shows one of the emails that someone else was able to forwarded back to me and that there are 9 messages that should be showing but are not.
ప్రత్యుత్తరాలన్నీ (1)
If the email was one in a thread, then it will show one email until the threads are expanded. But the count will show the number including all the threads.
So check to see if you have threads enabled.