[20240218]
Thunderbird config hints.

Once an email account is set up, when you have done a delete, you'll get a 'Trash' folder.
Right-click on this and take 'Properties'.
Across the top, click on the 'Retention Policy' tab.
Deselect 'Use my account settings'.
Select 'Delete messages more than' and set to 30 days.
Deselect 'Always keep starred messages'.
Hi 'Ok'.
Do the same for the 'Inbox', 'Sent', 'Archives' folder and any sub folders, except select 'Don't delete any messages'.