There is no option to change the location that I am aware of. I just turned the notifications off years ago, along with the annoying sound interruption.

The location, and many other effects, can be customized with this add-on:

https://addons.thunderbird.net/en-US/thunderbird/addon/mailbox-alert/

The location, and many other effects, can be customized with this add-on: https://addons.thunderbird.net/en-US/thunderbird/addon/mailbox-alert/

I'm afraid that this is not working anymore! I just sent a test email from outlook to the email address added to Thunderbird and the notification has shown in the lower right corner of the screen.

See the attached image for my Mailbox Alert settings

Thank you.

Tested as follows and it works for me.

I created same as you for 'Default Message' and also another test one named 'Manual Setup' At first it did not seem to work and I still got bottom right pop up.

Disabled the default pop up alert in Thunderbird as this is not required.

Then - right click on 'Inbox' folder and select 'Mailbox Alert > select 'Manual Setup' It now works on that folder.

Remove that setting for that folder - Right click on mail account name folder - select 'Mailbox Alert > select 'Default Message' and also 'Alert for childfolders(if they have no alerts themselves)

Sent email to me to test. Even filtered mail to other folders gets the alert as required. Pop up in top right. No default alert from Thunderbird.

I did not add a sound to the Mail-Alert - I just kept the Sound Alert I'd set up in Thunderbird as the default one and it continued to work. So you can keep the 'Play a sound' via Thunderbird Incoming mail Alert and use it with the Mail-Alert pop up.