Why is it not a good idea to sync Thunderbird profile with nextCloud?

The goal of this post is to get a technical theory about the topic.

It is often mentioned that you should not sync user profiles (e.g. Thunderbird user profile) with any sync/cloud service like nextCloud or ownCloud.

For example there is this bug report on Thunderbird where ownCloud could be involved.

OK a sync/cloud services bring new factors into the system. A more complex system gives a higher risk for failures. But this is theory not more.

From my technical understanding it should work.

Can you (as the developers) describe technical details what can go wrong in such a situation? Is there a technical theory that support the recommendation not to sync user profiles with nextCloud?

btw: Just assume the nextCloud is up and running. No network issues, etc

the file is big and we don’t have delta sync

this work in theory, but in practice a lot of data has to be transmitted when very little changes

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I’am not a developer and I cannot describe technical detail… But I can say that much from the time i’m working in IT:

Well… in your case it wasn’t just theory, wasn’t it? Sorry had to say that. :wink:

From my technical understanding it should work.

But in such cases it is often the details that matter. And between technically possible and reliable functioning is often a rather large gap. Closing such a gap often takse a relatively large amount of effort.

In other words…Even if it could theoretically work, some additional development work and testing would probably be necessary to be able to guarantee that it runs reliably in conjunction with a cloud sync client. “This use case is not supported” simply means that nobody has dealt with it in detail so far and therefore none of the developers can guarantee that there will be no problems with it.

Or to put it quite simply… If you use it anyways, you’re on your own. :wink:

Dear @ChristophWurst, the profile data does not have big files. This is because I do not use TB in its default mbox mode but in mail-dir mode where each e-mail is one file. Delta sync is not needed. All files are under 2 MB - even the folder index files (*.msf). Only exception are files with big attachments (<50 MB).

@bb77 It is not proven that ownCloud cause the problem described in the bug. What I miss is a theory about why and how it could affect the TB profile.

This post here is not about Thunderbird support politic. It is just about getting a theory. :wink:

I get that you want to know how it is working in detail. But other than getting a theory, how does it help you? I cannot see the benefit from using it like that anyways. Syncing is not a backup. And you should not use the same profile from multiple clints either, because it is not designed for that usecase and could cause problems if ever multiple clients use the profile at the same time. If you use Thunderbird as an IMAP and WebDAV Client you could simply backup your settings from time to time. The Mails and calendars stay on the servers anyways. If you want to make regular backups of your mailbox, there are tools for that.

This is because I do not use TB in its default mbox mode but in mail-dir mode where each e-mail is one file.

Ok I don’t know if Thunderbird still uses the database file for some things when you are in mail-dir mode. But suppose it is, in order for that to work reliably, Thunderbird probably had to implement some kind of file locking mechanism that locks the file whenever it syncs. At that point it would probably be easier for them, if they implemented their own WebDAV-Client.

I sync the profile folder not for backup but for using a POP3-configured-Thunderbird on multiple machines. Just for me.

POP3 because for security. It is (in my environment) unsecure to keep mails on the mail server.

I am not on two machines at the same time. This is impossible and my own responsibility. :wink:

You could set up something similar to this on a local server …


With a solution like this, you could use IMAP on multiple local clients without the mails having to be kept on the server of your mail provider.

POP3 is simply not designed for a use case where multiple clients have to stay in sync and therefore everyone will recommend you to use IMAP. But maybe there is a way to optimize the synchronization of the Thunderbird profile over several PCs. But there will hardly be a 100% reliable solution and certainly not one that works as conveniently as IMAP :wink: