How to sync local Thunderbird contacts with CardDAV (eg. Gmail Contacts)?

Question

I have discovered that Thunderbird has at least two types of address books for storing contacts:

• local address books: Collected Addresses, and Personal Address Book
• remote address books, eg. Gmail or Zoho Contacts, via CardDAV

Remote address books get synchronized via the CardDAV server, so the contacts in those address books are automatically kept consistent across any devices and Thunderbird setups using CardDAV.

But how can the local address books be synced? Ideally they could be "merged" or "synced" (not just copied manually) with one or more of the remote address books to let CardDAV do the rest. Can this be done?

Another thought is to use file syncing, like SyncThing, to keep the local address books consistent between Thunderbird on different devices, but I'm apprehensive about file conflicts.

What are the best ways to keep Thunderbird's local address book contacts synced across devices and/or with other remote address books?

Answer 1

Not having found a perfect solution, the most practical approach so far has been to:

1. Manually move all contacts from the Collected Addresses and Personal Address Book to a remote address book that uses CardDAV
2. Change the address collection setting from a local address book to a remote address book in Settings > Composition > Addressing > "Automatically add outgoing email addresses to my:"

This takes care of outgoing email addresses. Not clear what happens to incoming ones.