An article of Bill Thompson from BBC World touches on the unsecured nature of email.
And that reminds me of how its easy to trace an email message.
Tracing Email 101

from Bill Thompsong article

Every time you send an email it passes through a series of computers on its way to the intended destination. Most of them are owned and managed by internet service providers, although if you use webmail from Yahoo!, Google or Microsoft then it may take a different route.

But whoever provides your email, the chances are they are having a look at every message you send or receive.