I'm going to add that while you may
want privacy with regard to e-mail as a general rule it's
not private at all on the Internet. E-mail can be intercepted in transit and read (it's in plain text) and the mail admins of whoever hosts your e-mail can always get in if they want to. Never, ever send anything sensitive via e-mail ever. This included work e-mail or personal e-mail.
Bigger companies can host their own e-mail and the internal messages are relatively secure (from everyone but the admins) but when messages leave the company and get on the Internet there is no expectation of privacy. At my last job I was an e-mail (and everything else) admin and the rule was never look at an employees e-mail unless the owner was over your shoulder telling you to (it's technically all his anyway) but there was no real way to enforce that rule.
You can encrypt e-mail but it may be more of a discouragement to your customers as most users have a real hard time with normal logon passwords.
If you need to collect private data from customers over the Internet I would suggest finding a hosting company that can setup a web-based form that is protected by SSL. That way you can direct customers to the web page where they can fill out whatever.
There are a lot of companies that will help you setup a domain name (i.e. a dot.com name) with e-mail and a web page for very little money. I think Microsoft even offers this service (i.e.
Microsoft Office LIve). Disclaimer: I've never used the Microsoft or any other service like this so do your own research!