For archiving purposes I'd like to store my emails locally in the MailDir format, so I can do incremental backups and have a granular defense against bitrot (one broken email compared to one broken folder when using mbox format).
I can change the storage format to MailDir for new accounts but not for existing. The existing Local Folders account exists from installation and is MBOX and cannot be changed afterwards. And also I cannot create a new Local Folders account which would be set to the MailDir format according to the settings.
Please help, how do I get a Local Folders account with MailDir?