How to synchronise Thunderbird between several computers

Thunderbird can not (yet) sync the profile across multiple devices. So for the time being you can sync emails via an IMAP server, contacts via a CardDAV server, and calendar via a CalDAV server. As an example, all of that can be done with a Gmail account. There are certainly other email providers capable of doing that as well

I honestly don't know how to go about doing that. I've never heard of CardDAV and CalDAV servers. It sounds like an awful lot of hassle for something I'd ideally want to do on a frequent basis.

I should just mention I use POP3 for mail on my PCs and IMAP on my mobile.

As Christ1 stated, you need IMAP to sync email messages. Your use of POP and IMAP will never work together. I encourage using IMAP on the PC as well.

I use POP because I prefer to keep my messages on my local storage rather than have it held on a remote server. I have Thunderbird set to keep messages on the server for 14 days before deleting them. That way when I receive them via IMAP on my mobile I have time to make sure they're downloaded before they're deleted.

I understand the advantage of IMAP, being able to access the data from any device anywhere at any time, but I prefer not to have my private data held on a remote server. You may not agree with that and I realise it's introducing complications with keeping the data on multiple devices but that's my choice.

I honestly don't know how to go about doing that. I've never heard of CardDAV and CalDAV servers. It sounds like an awful lot of hassle for something I'd ideally want to do on a frequent basis.

Google offers caldav and carddav as a standard part of a user mail account. So essentially Google acts as the central store and everything replicates from there. Yahoo and GMX also offer similar DAV services that I have used. I find Thunderbird struggles with the GMX non mail password storage for some reason prompting for passwords when it should be remembering them.

The setup for Google is included in the add a new account process these days but you can add a calendar "on the network" or an address book the same say and have then sync between devices

About the only major provider you can not use without addons and inconvenience is outlook, because Microsoft use proprietary protocols for that same things. ie acticsync on phones.

Hi Matt, Thanks for responding and sorry for the delay in acknowledging.

I've always tried to minimise my interaction with Google, difficult though that is. I don't use their search engine, preferring DuckDuckGo. I had to accept an account on my mobile to access the Play Store but I elected not to use the pre-installed Gmail and installed K9mail instead.

It's a pity the Thunderbird developers didn't give much thought to synchronisation across devices. I was hoping backing up the profile to a zip file then restoring it on another system would work but it seems the only way I could do this is by dumping a lot of my older data to get the file size below 2GB.

Oh, well, I think I'll just give up on the idea.

I've always tried to minimise my interaction with Google, difficult though that is.

Nobody suggested that this only works with Google. Google was just an example, as it's pretty straight forward to set up. You can use any other email provider who provides IMAP email, a CalDAV calendar server, and a CardDAV address book to sync your data across multiple devices.

The Thunderbird Sync feature is still in the works, and I don't know when it will be available. https://blog.thunderbird.net/2023/07/an-update-on-thunderbird-sync/

I've always tried to minimise my interaction with Google, difficult though that is.

Then you will have missed the Google AI offering the following including the service providers.

CardDAV (and CalDAV) providers allow you to sync contacts across your devices using open protocols. Top dedicated and privacy-focused providers include: Fastmail: A premium, reliable email provider with native, seamless CardDAV and CalDAV integration. Mailbox.org: A German, carbon-neutral, and privacy-focused provider with full CardDAV and CalDAV support. Posteo: Another privacy-centric German email host that offers secure contact synchronization over CardDAV.Nextcloud / ownCloud: Ideal if you want to self-host your own server or use a managed Nextcloud provider to manage all your DAV services independently.

Although the duckduckgo AI offers some of their preferred providers as well https://duckduckgo.com/?q=caldav+carddav+providers&t=h_&ia=web with next cloud appearing on both lists

I elected not to use the pre-installed Gmail and installed K9mail instead.

That is Thunderbird for mobile. I would suggest using Thunderbird for Android (A Google proprietary operating system) as development on k9mail has largely ceased with the release of the Thunderbird version. https://k9mail.app/2024/08/28/What's-Happening-With-the-K-9-Blog https://blog.thunderbird.net/

It's a pity the Thunderbird developers didn't give much thought to synchronisation across devices. I was hoping backing up the profile to a zip file then restoring it on another system would work but it seems the only way I could do this is by dumping a lot of my older data to get the file size below 2GB.

I just copy files I don't use the internal stuff to move a profile, but moving and synchronization are not the same thing. You appear to be conflating them here using zipped profile data. But sync has been under discussion for years, there has so far been very little to see but though for the last 17 years. I see Christ1 has linked to the blog copy from three years ago on the subject. Please refer to the bug for specific information including links to the ongoing work https://bugzilla.mozilla.org/show_bug.cgi?id=446444

Oh, well, I think I'll just give up on the idea.

As you please.