Possibly related to upstream bug: https://bugs.kde.org/show_bug.cgi?id=379131
See possible workaround there.
- Bug#885182: [kmail] KMail Does Not Receive Messages (IMAP) David Baron
- Bug#885182: [kmail] Time overdue to fix this stuff David Baron
- Bug#885182: Possibly related to upstream 379131 kde bug inkbottle
