I'm trying to configure Dovecot, it seems to be used a lot and has server side mail filtering which I like. However, all my folders are subfolders of the Inbox which seems to confuse the Android Mail client, which subsequently crashes when trying to view the sent mail. Can't figure it out!
I'm on a VPS that I control and have full root access to my chunk. Running a phone with Android stock email client.
The solution was the configure the inbox namespace to use no prefix, by default this is commented out and it would stand to reason that being commented out it doesn't need to be explicitly set to nothing.
Once I uncommented the default settings in the namespace and restarted Dovecot, it worked just fine. No more crashing in Android, the mail folders moved to be top level folders and not subfolders of Inbox.
The only problem came with Roundcube which had trouble seeing what mail folders were for what purpose. I had to explicitly set them via the web app, but that is likely because I had been using the same roundcube installation for testing and it probably just got confused.