Please tell us what the alleged "problem" is and you may get some advice about it. You can choose your own sound or turn it off entirely if you prefer.

As far as I know, this forum is users helping other users, and of course, we can't change the program. I'm not aware of the developers being present.

Personally, I don't have a problem with the sound. I use my own, which gets my attention but isn't obnoxious.

As I explained in another forum... For years, ANY SOUND I selected would reliably play with incoming mail. I've used the default sound, but mostly various .wav files from my own collection. NEVER had a problem. But, suddenly, NOTHING will play when new mail arrives. However, the 'test' function in settings works fine. I've tried every possible fix. Thanks.

I wouldn't know what you explained in another forum, of course.

In my Windows 10 and 11 setups, it's possible in the mixer app to control the sound from individual apps, including Thunderbird, separately. Maybe you have actually muted Thunderbird?

That's the first place I checked. It's properly configured.