Email client suggestions

I'm trying to decide on an email client, and my needs are far from typical. ;)

Things I need:
- view emails as plain text by default;
- handle multiple accounts simultaneously, with each account having its own inbox folder etc.;
- handle receiving a couple of thousand emails at once;
- sort incoming mail based on arbitrary headers;
- easily get at a message's headers;
- get at a message's raw form, ie showing all the headers, MIME encoding etc as it would have sat on the mail server;
- simply import/export to other instances of the same client (so I can move all my email across to my laptop before travelling);
- redirect a message rather than forwarding it (ie retaining the original From: header)
- search through multiple folders at once;
- minimise the program to a tray icon, not a full taskbar entry.

Things that would be nice:
- use LDAP as a source of addresses;
- some sort of optional short-term pop-up notification when new email arrives in particular folders.

Things I don't need:
- create HTML or rich-text messages.
- free.

Right now I'm using The Bat!, which pretty much matches all of that. However, they're trying to squeeze money out of customers yet again (2.13 beta just got released as the paid upgrade 3.0, much like 1.63 beta got released as 2.0), so I'm looking around before coughing up again.

Any other suggestions for clients I should look at? I have no problems paying for one if it does everything I need.