It depends on what was sent in the message and how your email is setup...
A simple email can have delivery confirmation, scripting, and/or embedded links:
Delivery Confirmation: Can be automatic email back or you OK--setup to require OK for DC's. Since many (most) emails don't have real return addresses, DC's are probably not used often for tracking real email addresses.
Scripting: Email programs can act like web browsers and execute scripts to do stuff--setup to disallow scripting.
Embedded Links: URL to image on another server (will give your IP address and computer type, can be encoded with number linked to your email address)--setup to disable embedded links.
I am using
Thunderbird (companion to FireFox web browser) for email... Most of this is defaulted that you need to kick "OK" have anyone outside of your computer see you "reading your email"... Also, Thunderbird does not natively support Active X and I have scripting turned off... Pretty simple setup and works just like Outlook Express--install will copy (not change) Outlook setups, addresses, and email folders to Thunderbird automagically.
-Bill