You can sort of do that using these directions to download your Chatmails to Maildir format and view them with Neomutt. Technically, though, that solution bypasses Deltachat entirely: Deltachat and Neomutt are two independent mail clients downloading the same mail from the same server in parallel.
I should perhaps write up a more minimal download-to-Maildir tutorial, though there must be some on the Web.
Thanks - well, not sure. Let me put it in other words:
The solution I marked as such is indeed meant and working for the classical (non-chatmail) setup where I own and access a mail account, to pull (old) mail on a file by file basis to a local mail folder, thus creating an infinitly working, incremental backup that honors the (limited) online mail account storage.
Concerning ChatMail: AFAIK the idea of ChatMail is that you do not use your own mail account but a foreign mail account instead, and that the servers (you donāt own) just play as mail relays (or forwarders). Is that correct?
And if so, I wonder whether it is possible to download mail from that foreign mail accounts at all?
If yes, the solution to create incremental backups could work like for the classical DC. (Well, it would be still a lot harder as there is just a short time the mail remains on the relay.)
If no, I completely fail to see a solution to incrementally āmoveā older messages to a backup and decrypt/read it from there for the foreseen future.
Of course, I hope there is a good (infinite) backup solution for ChatMail, too.
Yes, with Chatmail you use someone elseās domain and server (usually).
Relay and forwarder usually mean a server that sends the mails on to another e-mail address. Chatmail does not do that.
Yes! Historically, all mail was downloaded by the recipient. The POP protocol removed the mail from the server, storing it only in the local mailclient.
The later IMAP protocol left copies of the mail on the server and synced the local copies; it rose in popularity in the 1990s as people increasingly had access to computers at work and at home, and wanted to be able to access their mail from multiple computers. Webclients were even more convenient.
And then people began using only webclients, and not using local clients at all. And now we have Google making it really hard to use IMAP, and some providers, like Protonmail and Tuta.com, providing webmail for free but requiring you to pay money to enable IMAP if you want to download your mails.
But the default, efficient, standards-compliant mailserver allows you to download mail.
And you can download mails from a Chatmail server, using any IMAP-compliant mailclient (and I canāt think of a modern client that does not have IMAP support). I have tested this. It works.
Deltachat is also an IMAP-compliant mailclient. It gets messages via IMAP. So you canāt use a free Protonmail or Tuta account with Deltachat, but you can use any mailserver with IMAP. And anything that works with Deltachat can also be downloaded to anywhere using IMAP.