An embarrassing e-mail

I received a note from someone today, in reaction to my Tech Republic article on avoiding e-mail blunders http://blogs.techrepublic.com.com/helpdesk/?p=56.

This person had received, from someone he knew, a note in error. The sender did not mean to send it to this person, but rather to someone with whom the sender was having an affair. The person who e-mailed me wondered if he should have let the sender know, then concluded he probably shouldn't, because of the resulting embarrassment.

I don't know how to answer this person, so I'd like to get your comments. From my perspective, I see two issues:
- addressing and sending too quickly
The person mentioned in the email probably didn't check the address field. If they have predictive fill-in, it's easy to send a message to the wronge person.
- relying on e-mail in the first place
Putting such intimate thoughts in an e-mail is questionable by itself. One doesn't know if the note will be forwarded, and in addition, the contents of e-mail are generally open for being read by others. Rather than putting dangerous or sensitive thoughts in e-mail (and I'm not advocating that you have an affair), think about simply asking the other person to call.