Comment # 2 on bug 944768 from Michal Bruncko

I think that message "Error message: Server is unreachable (Could not connect:
Network is unreachable)" could be related to IPv6...
Location where SOGo server is connected supports IPv6 and DNS name is
resolvable to both A and AAAA records. But client side LAN does not support
IPv6 and I have just link-local IPv6 addresses configured over NIC adapter. I
think that Evolution-Data-Server is trying to connect using IPv6 once it
realizes that DNS name has AAAA records. This confirms also fact, that once I
changed DNS name to IPv4 address I cannot longer receiving "Error message:
Server is unreachable (Could not connect: Network is unreachable)" message. 
Interesting thing is that this happen only for Calendar and Task sections.
Address book toward same SOGo server is working fine with DNS hostname inculded
in URL.

Also I have tried to shutdown AppArmor in order to avoid possible security
related issue, but with same result.