And just to jump in on the converation (albeit, a bit late)... I'm pretty sure I would have handled the situation in a similiar fashion.

Jackie is right - we all have a nosy element in all of us.  It's human nature... I have to monitor my boss' email when she's out of the office.  Currently she's out for 2 weeks - so I'm having to monitor her mail a bit closer to avoid her coming back and having to go through 200+ unread emails (ohhh she sooo would not be happy!!)

I go through her emails, handle what I can, print out FYIs so she's aware of what occurred while out, etc.  Some emails don't have confidential in the subject line (I realize the case mentioned here did)... but in reading the email I'll see that it is an issue that's confidential.  In that case, I do not print it out - but leave it marked 'unread'.  

And I rarely discuss things that come through my boss' office with any co-workers...  whether they're confidential or not.  But at no point would I mention something I'd read marked confidential... even if what I read upset me, etc.  I might mention to my boyfriend, but even that's rare.  He's very understanding if I'm upset and all I can tell him is I found out privledged information and I have to sort it/process it because it upset me.  He never pushes to know what I shouldn't repeat.

Just my take on the subject.....