Message-Tracking: Return to Sender, but Not By E-Mail

For centuries, letter writers have wondered whether their missives safely reach the hands of their intended recipients. "I know not whether this will ever come to your hands or miscarry," opened a typical one in 1625, from Roger White in the Netherlands, who was writing to friends at Plymouth colony.

Today, of course, we send e-mail messages that travel great distances in seconds, rather than weeks. Occasionally, however, we do not hear back and wonder whether our message was ever received. Wouldn't we be grateful if we could know with certainty?

I'm blithely inconsistent, however. When I'm the recipient of an e-mail message, I'm uncomfortable when a sender, seeking reassurance of safe delivery, presents me with a pop-up box requesting that I click to acknowledge its receipt. I routinely decline to do so. Why? I can't say exactly. Maybe it's like the unpleasant business of being presented with a certified letter from an unpaid creditor.

Before the advent of a federal postal system, letters passed through the hands of many volunteer carriers on the way to their destinations. William Merrill Decker explains in "Epistolary Practices: Letter Writing in America Before Telecommunications," published in 1998, that letter writers were willing to "consent to write five letters on the chance that one might reach the addressee." When a letter was lost or delayed, it was said to be "miscarried."

So, too, can e-mail be miscarried. A message usually hops several times as it traverses one mail router to the next. The technical name is MTA, for mail transport agent. Each mail router can see only as far as the next hop. Once it hands off responsibility, it has no way to track the progress of the message.

The basic Internet e-mail standard -- SMTP, or simple mail transport protocol -- has always provided for the destination...