SUMMARY For a single (long used) account imap stoped working. If I switch to STARTTLS it works again and stops again if i switch back to SSL/TLS. In other clients and on my phone everything works well with SSL/TLS enabled. Some lines from the logfile: [2022-01-25T10:31:15.413Z] akonadi_imap_resource org.kde.pim.kimap KIMAP::LoginJob(0x5638e865d6d0) [2022-01-25T10:31:15.414Z] akonadi_imap_resource org.kde.pim.kimap KIMAP::LoginJob(0x5638e865de30) [2022-01-25T10:31:15.414Z] akonadi_imap_resource org.kde.pim.kimap Connecting to IMAP server with no proxy [2022-01-25T10:31:15.414Z] akonadi_imap_resource org.kde.pim.kimap connectToHost "imap.ionos.de" 993 [2022-01-25T10:31:15.439Z] akonadi_imap_resource org.kde.pim.kimap KIMAP::LoginJob(0x5638e865de30) [2022-01-25T10:31:15.491Z] akonadi_imap_resource org.kde.pim.kimap TLS negotiation done, the negotiated protocol is "TLSv1.3" [2022-01-25T10:31:15.586Z] akonadi_imap_resource org.kde.pim.kimap Received BYE: "out-of-sync data before server greeting " [2022-01-25T10:31:15.586Z] akonadi_imap_resource org.kde.pim.kimap close [2022-01-25T10:31:15.586Z] akonadi_imap_resource org.kde.pim.kimap close [2022-01-25T10:31:15.586Z] akonadi_imap_resource org.kde.pim.imapresource online= false [2022-01-25T10:31:15.586Z] akonadi_imap_resource org.kde.pim.imapresource online= true [2022-01-25T10:31:15.586Z] akonadi_imap_resource org.kde.pim.kimap Connection to server lost QAbstractSocket::RemoteHostClosedError [2022-01-25T10:31:15.586Z] akonadi_imap_resource org.kde.pim.akonadiagentbase Deferring task "977 Custom startConnect " [2022-01-25T10:31:15.586Z] akonadi_imap_resource org.kde.pim.imapresource online= false [2022-01-25T10:31:15.593Z] akonadi_imap_resource org.kde.pim.kimap KIMAP::LoginJob(0x5638e865de30) Maybe this is related to akonadi. But I don't know how to check that. STEPS TO REPRODUCE 1. Switch to SSL/TLS 2. Switch back to STARTTLS OBSERVED RESULT see above EXPECTED RESULT no error