If you have two or more workstations with thunderbird you will want to sync your messages, addressbook and calender. imap does the job for emails. Webdav, Dropbox or Livesync does it for your calenderfiles and could possibly do it for your adressbook too, but there is an native solution by an addon: Addressbooks Synchronizer can sync your adressbook through a bunch of ways. i prefere imap, so there is no dependency on an other service than your mailserver and the transmission is encrypted by the transportlayer. https://addons.mozilla.org/de/thunderbird/addon/2533/