[vog]

> That Outlook (of all programs!) is the only tool that I know of that makes this easy

Not sure what you mean.

It works as easy with Mutt. Open IMAP folder, select all, save to [other IMAP folder or local folder, as you wish].

Works reliable even with very large folders, you just have to wait a bit longer until it's finished.

[Normal_gaussian]

Practically every email program can move email easily. It is somewhat trivial.

Recently we moved all our company mail with IMAPsync. Automated commandline tool. Awesome.