Why? Because different relationships call for different means of communication.

• Lovers, parents, and children want to connect as intimately and immediately as possible -- real-time, multisensual, and with perfect fidelity -- which is why the military sets up video calls for overseas troops.
• Young people prowling for life partners want to maintain their networks via frequent (incessant?) touches with a large group. Users like this IM "sup?" a hundred times a day and Tweet every aggravation, no matter how petty.
• Businesses want to coordinate their work yet control the flow of information. Their messages are more formal and hierarchical. When two executives don't rank equally, real-time conversations demanding input and decision-making aren't always desirable. If the guy in the mail room has the courage to send a suggestion to the CEO, he's not going to use IM. He's going to use e-mail.
• And e-mail excels in its function as an anti-boor shield. Who wants more real-time conversations with self-indulgent time-wasters? Who wants bill collectors, direct marketers, or religious proselytizers setting up camp in their electronic living rooms? Hurray for auto-reply, filters, and the delete button.

E-mail is the misanthrope's best friend, the key passive-aggressive management tool. Anyone who's ended an affair by leaving a kiss-off on the answering machine of a soon-to-be-ex would rue the decline of e-mail. It's also perfect for those on different schedules, or in different time zones: the exchange may be protracted, but it's still convenient.

The next time you're trapped in an unending IM session, ask yourself whether e-mail might have worked better. Disengaging from e-mail means never having to end the conversation rudely. Just because we can have real-time conversations involving multiple users with video links and embedded video doesn't mean we'll always use every bell and whistle. When we only need to press a thumbtack into a wall, the heel of our shoes work better than a hammer.

I hope that we're evolving toward a world in which we have a perfect answer for each communication problem. And while I embrace our new technologies, I don't think that any method can ever be one-size-fits-all. E-mail, by some name, will still find a place in our future communications -- even if it's the same place where we put our postcards or our billets doux.