This page is for people who think that I sent them unsolicited email. Here's how to tell whether a message is really from me or not.
Typically, messages from me are either about entomology, or about computers. If you received a message from me about something else, like "Visit my cool w3bsite now!!!" chances are that it's not from me.
All email messages carry with them a trail showing where they originated. Here's what a legitimate message from me will look like:
Note that the first "Received" header (the one lowest down in the message headers) shows that the mail message was received from a machine at Iowa State University, where I work. You can tell this for two reasons: (1) "matilda.iastate.edu" is a machine in the iastate.edu domain, and (2) the IP address given begins with 129.186, which is Iowa State University's network. Further, you can see that one of the mailout.iastate.edu servers (in this case mailout-1) received the message and passed it on. So, the following clues allow you to conclude that I sent the message:
Here are some hallmarks of a message that looks like it came from me, but really didn't:
Note that although someone has filled in my email address for the Return-Path and From headers, the message is not actually from me. How do we know? Because in the first "Received" header (the one lowest down in the message headers) we see that the message originated from a machine with IP address 126.96.36.199, which is a South African network. Secondly, the mail server that received it is mta118.mail.re2.yahoo.com, a mail server at Yahoo!. We can thus conclude that this email was not, in fact, sent by me.
Why would someone do this? Why would they put my address in the From and Return-Path headers? The answer is that whoever did it does not want to receive replies to the email they sent. They probably want to get the message out about some new website they are promoting, or convince you to click on a URL in the message that will infect your computer with malware.
So you've probably reached the following conclusion on your own: it is useless to reply to unsolicited messages. Your reply will doubtless go to someone whose email address has been forged, without their consent, in the the message you received. The best thing to do with unsolicited messages is to either ignore them or, if you've got lots of energy, prosecute the spammers. But in any case, it wasn't me...and now you know how to tell.