On Win 11 (and probably Win 10) new message notifications in the Windows sidebar should be batched to reduce unwelcome distraction to the user.
Currently, each mail triggers a notification which is OK if you receive one or two messages but if e.g. 20 messages are received one after another this creates many notifications one-after-another which is distracting and annoying.
For me, this behaviour happens when the computer wakes up in the morning and starts picking up dozens of emails that have arrived overnight. Each email produces one notification message in the sidebar + the sound for new message. It is extremely annoying to the point of switching the notifications off.
Instead I suggest that Thunderbird either:
1. Looks up the count of new messages in the email account; if more than one message is found then issue only one notification saying e.g. "You have 10 new messages from x, y, z" (or just "You have 10 new messages at joe@example.com")
2. If new message count lookup is not possible, then debounce the notifications. When new email is received wait e.g. 5-10 seconds before creating a notification in the sidebar. If during this waiting period there are no more new messages - issue a single notification; if more than one message is received you can wait some more or issue a combined / batched notification.