It's a cash crop, I contend. Ah yes, here come the thunderstorms. Sending e-mail is just about as simple as receiving it. Sometimes, however, people don't respond to your messages. They may not feel the need to reply, or you may have botched up YOUR return address.
Chances are, there's been a misspelling.
Double check your settings. In fact, let's put a spin on this. You can initiate an e-mail to someone, and when the recipient replies, that response will go to another person. The applications for this tactic are limitless.