Unless your E-mail providers are absolute retards any connection you make to your IMAP server is an SSL/TLS encrypted tunnel which is unreadable by 3rd parties.
We had an experimental automated dispatching system for we Field Engineers last year. We were all issued with Blackberrys and they became a real PitA. Apart from the fact that the dispatching application couldn't find its way out of a paper bag unless someone shone a light, the email application was quite useful. Given that our server is so anal it won't allow mention of a well known North East coast fishing port, it will only allow public key encrypted email transmission.
When the experiment ended, after six months of pain and irritation, it was, needless to say, declared a success.
The Blackberry's were collected and there was talk of us being issued iPhones - until it was found the iPhone will not support any form of encryption. If you use iPhone with your email, it is, by definition, unsecured.
Roger.