Postbox
From Indie IT Wiki
Postbox is commercial fork of Mozilla Thunderbird.
INFO:
Thunderbird Extensions Found To Work With Postbox
While a fork of Thunderbird there is no guarantee that extensions created for it will work with Postbox, it is more a case of trial and error.
The following are ones that have been found to be compatible with Postbox 4.0.3:
HOWTO: FIX:
Failure Of MAC OS X Contacts (Address Book) Integration
This traces back to a value not being written to the configuration file after authentication Thunderbird in System Preferences | Security and Privacy |
Config name: | ldap_2.servers.osx.description |
Value: | Mac OS X Address Book |
Thanks to Metaparadigma, which while not the actual solution above pointed me in the correct direction.