Re: [Evolution] Migrating from Thunderbird via import without duplicates

[Milan Crha <mcrha redhat com>]

On Wed, 2020-10-28 at 00:31 +0900, christopher wrote:
> Then what exactly is the use case for importing from Thunderbird as
> per [the manual]

        Hi,
I do not think Thunderbird import imports also local caches, it imports
local accounts only (from the Mail part).

> As I have between 50 - 100 GB of mail to sync, with it all backed up 
> locally, I'm happy to try to break things in an effort to avoid days
> if not weeks of re-syncing.

That feels like a lot of mails, or just few movies as attachments (just
kidding). Do you know how many mails this is? My largest IMAP account
has 498.162 messages at the moment, which is surely less than that
yours. I do not download all of the history locally, only the last
month is stored for the offline use, and even that not in all folders.

Note the initial synchronization doesn't download the messages, it only
downloads the headers (it depends also on the "Copy for offline
operations" option for the account and respective folders), thus it
should be significantly less data to be downloaded. Still, it takes
time and bandwidth. 

>  Are there details on this process (warnings heeded) anywhere?

No, there are not, because nobody did it yet and should not do that.

I can think of only a single workaround:
a) mimic exact folder structure under On This Computer
b) import the respective .mbox files from Thunderbird to those folders
c) add an IMAP account
d) close Evolution while it is synchronizing the data
e) copy ~/.local/share/evolution/mail/local/folders.db file into
   the IMAP's directory ~/.cache/evolution/mail/<account-uid>/; it
   will overwrite the existing file
f) run Evolution

This only *tries to* not download the folder summary data, but the
format of the On This Computer and of the IMAP is not exactly the same,
there will be missing parts, which may or may not cause trouble. It
does not restore respective messages, the cache format is different.

I cannot tell whether it'll work or not. I cannot tell whether it'll
have any side effects or not. I cannot tell... It's all up to you. I
would not do this myself. I'd rather "waste" the bandwidth to have
things as they are supposed to be.

Note that the IMAP (and any other remote account) has the data stored
in ~/.cache/, which is a disposable place. When anything happens to the
data there, the mail provider will re-download it from the server.
        Bye,
        Milan