Regrettably, today's popular e-mail clients don't provide a way to turn this feature off. It's therefore incumbent upon you to be careful. The easiest way to do so is to simply never say anything in e-mail that might offend someone, regardless of who reads it. But what fun is that?

Instead, you could make it a habit to always type the full e-mail address of recipients rather than relying on the Autofill feature, or you could let Autofill entries appear but deliberately click on a name in a list rather than pressing the return key to automatically enter an address. If you also look long and hard at every address in a message's To field before clicking on the Send button, you should avoid future embarrassment.

Another option is to assign nicknames to contacts you're likely to confuse. For example, if Justin G. works in the mailroom and Justin K. puts in his hours operating the office copying machine, assign the G.-man the nickname "mailroomjustin" and the other Justin, "copycat." To do this in Address Book, just select a contact's name, click on the Edit button at the bottom of the Address Book window, and then enter a name in the Nickname field. When you type the nickname in a message's To field, Mail will swap in the e-mail address associated with it.

Dear Mac Manners,

THIS IS THE THIRD TIME I'VE WRITTEN TO YOU, AND YOU HAVE YET TO REPLY!!!! IF THIS IS THE KIND OF DREADFUL SERVICE YOU TYPICALLY PROVIDE, YOU CAN FORGET ABOUT NEXT YEAR'S FRUITCAKE!!!!!