Ask HN: Any decent email backup viewer around?

There is a nice "IMAP Email Backup" thread nearby which misses one point: once the backup is done, how can I look into it?

I have a couple of large cloud mailboxes that I backup locally using getmail python script. As I don't want to keep everything online for life, the plan is to eventually delete the old emails from the cloud, leaving only the offline copy.

So what I need is the software that lets me comfortably read these offline emails like I do now. No edits, no replies, just plain read-only maildir viewer with fast search. Another complication is that the backup is on the NAS and I would prefer to access it by SSH instead of shared folder.

The next big thing is search. Without indexing it takes way too long to look through 200K emails, so I currently run mu indexer (a part of mu4e) that indexes the database after getmail, so I can do fast search queries using command line.

What I want is to provide a list of mu queries - as "filters/folders" to the application that does those queries for me and displays the list of emails and preview, like a standard email client. Anything like that around?

Or maybe there is a way to setup an IMAP server that uses the maildir and the index to serve emails into my email client with fast search?

I tried mutt, but it changed every email I viewed, so getmail was not happy about that. I haven't tried Thunderbird yet, but I think it will mess the maildir, as well. I am sure Emacs can do that, but I am not (yet) ready :)

I can't believe I am the only one who wants to easily look into backed up emails. Ideas?