One possibility is a service I joined while I was still at GoDaddy, where they don't have IMAP, and that's http://www.webmail.us. They specialize strictly in business-oriented email, and offer the proper level of security, plus a home-built Web email client and spam and virus protection.
I would recommend them heartily if you need something a little more robust than a Web host's email package.
Co-Host, The Paracast
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