After update to 1.1.15, I notice that rouncube was displaying error "connection to storage server failed", I check the logs and I found " s=deferred
(temporary failure. Command output: doveconf: Fatal: Error in configuration file /etc/dovecot/dovecot.conf line 83: Unknown setting: ss l_protocols ) line 83 is ", the line is "ssl_protocols = !SSLv2 !SSLv3 ".
Solution, comment that line and restart dovecot service.
The issue is about # Prohibit usage of older and deprecated SSL protocols mostly due to the POODLE
# vulnerability CVE-2014-3566
ssl_protocols = !SSLv2 !SSLv3 parameter is only available in dovecot > 2.1
In my scenario, Ubuntu 12.04LTS, dovecot version 2.0.19