As a followup to my article Replicating IMAPs (dovecot) mails folders and sharing (through ownCloud) contacts (kmail, roundcube, etc), I’d like to point out that, these days, I almost completely dropped Kmail (only use it on a laptop, mostly because I do not use the laptop frequently enough to bother) and switched to Thunderbird.
Using Thunderbird enables me to use cool Firefox modules like S3.Google Translator (note that Kmail also has a similar functionality) and works decently with modules Lightning and Inverse Sogo Connector for proper CardDav and CalDav handling. I went away from Kmail due to still existing akonadi issues after so many years and the fact I was still forced to run ‘qdbus org.kde.kded /modules/networkstatus setNetworkStatus ntrack 4’ after suspend for it to notice network is on. In general, I do not think KDE people are going in a direction that makes sense for me and Kmail was almost the last piece of KDE I was still using (since they more or less killed Konqueror themselves). I still enjoy Dolphin though, especially for the group results and filter bar.
Regarding Roundcube, CardDav is nicely handled by RCMCardDav even though it requires a bit a work to properly deal with dependencies.