I am planning to setup a groupware server that's either Citadel or SOGo, which supports the GroupDAV, CardDAV, or SyncML protocols.Is there a commandline e-mail client that supports syncing contacts via such protocols either out of the box or with a plugin/extension?
Commandline e-mail client that syncs contacts with external server?
command line;synchronization
According to the documentation of both of the software products you linked to (here and here) both support storing directory information using LDAP.  If you do not find a command line email client that supports the protocols that you mentioned, you could try using LDAP instead.  Every decent email client supports LDAP.