Who is snooping on my email? – Privacy guru Richard M. Smith explains how to tell if someone is reading your email, and perhaps even whom.
You'll need your own web page, with access to server logs. Plus you'll need to be willing to have a file on you, if you don't already. (And for the last step you'll need snoopers dumb enough to use a traceable IP number.)
The problem with that technique is it will cause a lot of false alarms and paranoia. People who THINK they are applying it correctly will make mistakes so that the “secret” URL is exposed somehow, and then believe they’re being spied on.
Just ask Judge Kozinski if you don’t believe me …
It would be so much easier to just use a secure email service that can prevent people from eavesdropping on your email. Several providers offer such services. A discussion and comparison can be found at novo-ordo.com.
Seems like you might just be giving them a reason to actually start snooping.
I like the idea about secure email though. at times I would like to email things to clients, that I would prefer not to get intercepted, passcodes and the like. I usually end up using the phone instead.