RPM of the new version of Mozilla Foundation messaging client is available in remi for fedora 14 and enterprise linux 6 (RHEL, CentOS, ...). This is a backport of F-17 version.
Start by reading :
As always:
yum --enablerepo=remi update thunderbird\*
enigmail (version 1.4.1) extension are also available.
lightning is no more available.
RPM of version 12.0 are availalble for fedora 14, and for enterprise linux 6.