Hi, does anybody here use MacOS Catalina Mail?
It seems that I cannot create/access Maildir subfolders (i.e. folders inside folders) at all. Subfolders created in Mail show up as .folder\2esubfolder on disk, suggesting that Apple Mail is URL-coding the dot separator before it passes it onto Dovecot. No such translation takes place when interpreting the IMAP tree though, resulting in subfolders rendered as plain entries with the dot separator preserved.
Subfolders can be created elsewhere (SoGO, Roundube, Thunderbird) just fine and work here just fine, suggesting that all is well in terms of Dovecot configuration. Subfolders created here though show up as a proper hierarchy in Apple Mail, but their contents is now displayed, so the user thinks the subfolder is empty.