Syncronization: How can i store mail for different accounts remotely, and copy most important mails manually to local folders on two devices?

Question

Hello. I have two devices and two accounts, so what i want is this:
I only want to store mail from both accounts in a remote place and copy most important mails to local folders.
(I will be grateful for any ideas as to where/how this "cloud" can be - specially free places)
* Can I have a copy of these local folders in both devices and the remote storage?
* Could i synchronize devices so that: when i move a mail to a local folder in any device, its copied to the same folders in
the other device and the remote storage place?
* The remote storage place will have many other folders. When I open Thunderbird, I also want to see these and the mail
inside, and also be able to move mail from the inbox to these folders.
* One of the accounts is gmail. In Account Setting tool, there is an option for synchronization. If there is no easier way, I can have mail for other account copied to gmail, and just syncronize gmail mail. For this, how will I copy my present folder structure to gmail. And how can I syncronize the local folders on the two devices?
Thanks in advance.

Answer 1

The first awkwardness I see is that there's no obvious format in which to store messages remotely such that you can work with them in an email client. It may be possible to set the "Local Directory" option in the account in Thunderbird to point at some remote folder (DropBox comes to mind) but I have never tried this and I'd be nervous about what happens if connection can't be made, or if you happened to access it from two different places simultaneously. The other concern is that mail stores get big, quickly, and you'd be forever uploading and downloading large (multi gigabyte) files. Thunderbird stores what looks like a folder containing many separate messages as one big file, so there's no simple opportunity for incremental changes to be up/down loaded.
The whole idea of Local Folders in Thunderbird is to detach messages from servers, so they don't track what happens on servers. I say this to point out the distinction between files stored locally and permanently ("Local Folders"), versus cached copies of online files ("synchronized"). It's not safe to regard your synchronized folders as permanent.
So, synchronized folders on an IMAP server are "mirrored" in Thunderbird so you do have a local (albeit temporary and transient) copy of messages; this is done mainly to avoid repeatedly downloading messages if you re-read them, and it makes searching faster an more efficient. But these "synchronized" message track what's being done on the server, and so if they are deleted anywhere, all synchronized devices will at some point also see the deleted messages vanishing. (Unless you made a local copy in the Local Folders account.)
I use a gmail account pretty much as you have described; I copy or move messages to that account so they are visible in my phone, my tablet, my own laptop and my works computer. It's free, and it's "in the cloud"; the only reservation I have is its privacy. There are other providers (e.g. 1&1/gmx) who don't seem to have the data collection fetish that google thrives on.
It's fairly simple to create filters in Thunderbird to automatically copy messages to your "cloud account"; even better is to set up forwarding rules on the other accounts' servers, so your messages are automatically sent on and waiting for you when you next login, already in the cloud account.