I tend to do a lot of emailing. I've used the same email address for about seven years now, so spam is a fact of life. I also get a lot of "service" related email (Netflix, online bill payment, etc) so keeping it all organized is important.
For the past few years, the ultimate destination for my mail has been Oddpost. Oddpost offered a webmail interface like no other, IMAP access, and enough storage to meet my needs. Back in July 2004, however, the nice folks at Yahoo! acquired Oddpost and little has changed since then. The service works well enough but is rather slow at times and the reliance on Internet Explorer is somewhat problematic. When Oddpost was created, that may have been acceptable, but I much prefer Firefox for day-to-day browsing these days.
Through a series of links I can't recall at the moment, I recently discovered Fastmail. Described as "the most powerful email system on the planet", they do a great job at email. The webmail interface is not as pretty or easy to use as Oddpost, but is much faster and offers SSL encryption.
Fastmail also provides IMAP with IDLE support. IDLE allows IMAP clients to remain connected and receive notifications when new mail arrives. If you've ever used Outlook with Microsoft Exchange, you will be familiar with how email simply appears in your inbox on arrival - there is no manual (or scheduled) "check mail" command. IMAP IDLE allows pretty much the same thing. With Mozilla Thunderbird, new mail appears in my inbox as soon as the server receives it. Even better, using Chatter Email on my Treo 650 allows Blackberry-like "push" email wirelessly. Cool stuff.
IMAP over SSL and authenticated SMTP over SSL is also supported, so I can securely login to my account from anywhere. A rather powerful filtering system allows me to keep mail folders organized, and thus far the spam and virus filters have been excellent. And, as their name implies, the service is fast to send and deliver email.
While I look forward to seeing what the Oddpost people are up to, for now, it looks like Fastmail will serve up my mailbox.