I've been looking for a while but haven't found one yet that says they don't save your IP address. Hushmail included. If given a court order in british columbia they will furnish what they have on you. The good thing of hushmail is the whole session is SSL encrypted, so at least if you go there from let's say, work, your emails to/from providers that you submit/view on the web page and stuff won't be in the clear on your LAN. So I'd say that's a required minimum.

I also found safe-mail.net which has its mail servers in Israel and the sessions are SSL. So if you're so paranoid about subpoenas maybe it's more difficult for the US authorities to get one through Israel's courts? I'm no lawyer so I dunno.

Now, ideally I think, you can find an anonymous proxy server that supports SSL connections, and then go to the mail server via proxy. That ought to hide your IP address. I haven't looked hard for that. How careful need one be?