WE SEND e-mail under a tacit, technical trust: that it will arrive. But more of my e-mail has gone astray in the last year than in the 25 years that came before. (This Babbage is an early adopter.) And a poll of many friends and colleagues says my experience is both common and recent. E-mail is losing its predictability.

It used to be that if mail failed, it bounced. Using the Tibetan book of the dead, e-mail header specifications and a knowledge of geography, I could sniff out what had gone wrong from the daemon that replied: a dead server, a misnamed domain or a user who left the company. In 1996, an editor's email arrived five months after he had sent it. Despite his IT department's protestations that it was impossible, the mail headers told the story of a long hiatus. Perhaps the waystation server that was a link in a chain was decommissioned, sent on a long boat ride, and powered up in Kuala Lumpur.

But now e-mail sinks without a trace. Nearly all of us sit behind a wall of filters designed to ferret out the latest, constantly evolving responses to spam detection. My server and client filters together capture 99.9 percent of illegitimate mail. Mail that can't beat the gatekeeper may be bounced, but more typically is filed away into a folder that we are expected to review at our leisure for false positives, or “ham”.

Many of these filters now use Bayesian statistical analysis, which scores an incoming message based on choices the intended recipient has made in the past. Messages that look like what's been marked as spam are likely themselves to be spam. But spammers have access to the same tools, and can analyze their own e-mail to create messages that score as low as possible. And Bayesian-based filters are just one tool. Examining the filters in spamassassin, a popular open-source effort, reveal quite a bit about the fight in progress. “CHARSET_FARAWAY” looks for email encoded in a language not your own. “BANKING_LAWS” looks for a message that "talks about banking laws." Both rules fight the last battle.

We should still be slightly behind the spammers, reading the small percentage of their most creative efforts that actually get through. And yet, from my own experience and stories I hear from fellow hoary internet veterans, something has broken. Many dozens of emails I've sent in the last year have never reached even a recipient's filtered folder. A few weeks ago, a note about compensation failed to reach the editor of this blog. (Yes, I believe him. Why do you ask?) Likewise, many messages never arrive into my inbox or spam folder. No rejection message arrives, to be decoded; no ham waits to be discovered among the spam. Mails are simply disappearing.

Your theories are welcome, but I believe that the complexity of getting through a spam-filter maze with ever more dead ends is a key cause. When you put together many rules and different systems, some of which are not specifically designed to work with each other, unexpected properties emerge. This is much how intelligence may work, at a vastly more complicated scale. But certainly, emergent properties make it difficult to predict how a given input will be output.

But this is not all bad. We can embrace e-mail's emerging ambiguity. If a sender can never know whether we received a message, the social expedient of "I'm terribly sorry; it must have landed in the bin" remains a viable white lie. (Editor's note: that e-mail about compensation truly did not arrive.) It could be, though, that there's a simpler cause. My e-mail may have become "tb;dr": too boring, didn't read.