How to make static copy of IMAP mail
I have an IMAP account with a large volume of messages and attachments. My access to the account may be going away and I want to freeze a copy of the emails. Ideally this would be so that I continued accessing it through one Thunderbird instance where the account looked identical but instead of fetching the messages from an IMAP server, they were all stored on local disk. I do not think that I have this automatically right now, since I believe it hasn't downloaded every message from the server.
If this local copy also allowed me to delete messages from that store via Thunderbird that would be great, but not essential.
Searching for something like this just leads me to pages about the offline mode. Not what I want. To recap, I want to download all messages and attachments from a particular IMAP account to one machine and access them via the Thunderbird email account interface as though the account were still live, but read-only.
Wšykne wótegrona (3)
It is a shame you have lots of folders as I am thinking each will have to be exported individually. As you say you can not be sure all messages are downloaded use the import export tools addon to export the messages in the folder as EML. You will need to preprovision the destination folder. The tool will check the folder is up to date with the server and also check each message as it is exported.
https://addons.thunderbird.net/en-US/thunderbird/addon/importexporttools-ng/?src=ss
Note that you can re-import the EML files using the same addon to local folders, and you can even call it what you like. This is the most likely to get you all of the mail. Other options like copying existing mbox files (Thunderbird folders) are not as guaranteed.
Thanks - I am unclear where I would be exporting them to. A different account on another server? Or backup files that couldn't be used without importing them to a different account? I think what I want is a virtual account type that maps to a local file store. If I then copied all the messages across to it with drag and drop, then I would think it would have to copy everything?
Your original post's idea would work. Download to local PC, store in the Mail\Local Folders folders and Thunderbird would have full access to read.