Retrieving mails from mailbox.org did not work. No inbox and other folders were displayed and no mails were retrieved. Connection to the server was ok according to Akonadi. Akonadi gave the following message: Hierarchical RID does not specify an existing collection. The following solution solved the problem: the folders with square brackets were stripped of these brackets. - Server side subscribers are disabled - Login is via SSL - port 993, plaintext See: https://dev.kampfq.eu/2019/01/03/kmail-ruft-keine-mails-ab/ mailbox.org works on the basis of OpenExchange. IMAP is integrated via IMAP protocol. SOFTWARE/OS VERSIONS Linux/KDE Plasma: Manjaro KDE Plasma Version: 5.22.4 KDE Frameworks Version: 5.84.0 Qt Version: 5.15.2 ADDITIONAL INFORMATION: mailbox.org ist E-Mail Provider with officesuite (Openexchange)