One of the things that I use to keep emails going the right direction is the 'nickname' feature that my email programs all have. I usually put someone's last name in - since last names are typically more distinct that first names (Okay, so I know like 15 Davids). That way when I type in the name, I'm certain that its going to the right person. As well, mistakes do happen. But taking responsibility for the mistake and handling it gracefully go a long way towards improving your reputation. Own up to it immediately, send an apology as soon as you discover the mistake - don't wait for a response from the other person before you act (unless you don't realize what you've done, then respond as soon as you learn). If you can find some way to add humor into your apology, that always helps.
-Centaura