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Credit Stephen Savage

Every new technology is amazing, and every new technology brings its own horrors. For example, there was no such thing as waking up at 30,000 feet on the shoulder of a stranger who is covered in your drool until we invented commercial air flight (and Ambien).

And so it is with one small email “feature” that we cannot do without, yet has cost almost everyone who has ever texted or emailed a moment of heart-stopping panic. I’m speaking of auto-fill.

It is often confused with auto-correct. Here’s the difference: Auto-fill fills in names and information based on just a few keystrokes; auto-correct does, too, but it also corrects (and predicts) writing in the body of a note.

For example, if I want to write to my editor Didi Gluck, I type ‘Didi” in an email and auto-fill gives me the rest; If I am writing her name in a text to someone, well, other things may happen. “Did you know ‘Didi’ auto-corrects to ‘dildo’? Because I do,” Ms. Gluck told me, cheerfully.

In some ways auto-fill may be the more problematic function, leading to not just semantic misunderstandings but to entire passels of information being dispatched to the wrong people. Secrets are disclosed, petty true feelings are revealed, words (and, worse, photos) of longing and lust end up in the email box of your boss instead of your lover. And no one is immune.

Several months ago Mayor Bill de Blasio of New York complained in an email to a few staff members that taking one of those I’m-a-man-of-the-people subway rides to an event had made him late. The mayor mistakenly included on this grumpy email thread Michael Powell, a reporter for The New York Times who for years covered city hall.

The result? A perhaps unwelcome article about the mayor’s chronic lateness. “I almost deleted his email because the sender only identified himself as ‘B,’ ” Mr. Powell said. “That struck me as suspicious, like perhaps it was one of those Nigerian or Croatian bankers with a grand idea, if only I’d send my bank account number.”

Slips like these remind us that Sigourney Weaver — No, wait, I mean Sigmund Freud — is alive and well and living in our keyboards. Just consider how frequently we send emails to precisely the person who should never ever receive them. It’s sending your estimated yearly tax income to an old frenemy, who has a similar name to your accountant; it’s getting out the word to friends that you need a new job and including your boss on that thread.

For Britt Kazmac, a New York City tutor, it was the all-too-common erotic message debacle. “I thought I was sexting my husband,” she said of her now ex-husband, “and he was playing coy by responding with texts like, ‘Why are you sending these to me?’ Then I looked more closely, and realize I had been sexting my daughter’s Charismatic Christian babysitter.”

Ms. Kazmac believes she has a gift for this type of spectacular misfire. “After a bad third date I wrote to my best friend, Donna: ‘What a waste of a bikini wax,’ ” she said, adding to the update, “Worst sex ever.’ It would have been nice if her best friend had received it; instead it went to the only other Donna in her address book: her graduate-school professor.

Or take this cautionary tale from David Hirshey, an editor at HarperCollins. Mr. Hirshey had paid seven figures for a celebrity memoir, and was getting constant interference from the celebrity’s manager. In a moment of desperation and frustration he sent out an email to his colleagues with the heading A Few Wise Words from Brain-Dead Manager. One of his colleagues and the manager shared the same unusual last name, and guess which one ended up on the email?

“Two minutes after I sent this, my phone rang and I heard the person on the other end say, ‘Please hold for brain-dead manager,’ ” Mr. Hirshey said. “Needless to say, this woman was not amused and made the rest of the publishing process a living hell for me.”

Even if we become more cautious in our day-to-day emailing, we sometimes forget how auto-fill works in programs we use less regularly. We’re not quite paying attention to the rules, as Laurie Lewis, a real estate broker with the Corcoran Group, found out recently when she joined LinkedIn.

“LinkedIn ‘asks permission’ to access your address book,” Ms. Lewis said. “I said yes. And then, unbeknown to me, it automatically selects everyone.” She ended up sending a request to everyone she had ever known, “including and especially people that I would literally cross a street to avoid.”

“LinkedIn auto-filled my worst mistakes,” Ms. Lewis said, “and reconnected me with all of them.”

There is a flip side to auto-fill, when we are not the perpetrators of a gaffe but the unwitting participants, caught in email chains we have absolutely no business being in.

“This happens a lot if you have a really common name like Ann,” said the writer Ann Leary, who has borne gleeful and illegitimate witness to various high-stakes real estate deals and publishing negotiations. Recently Ms. Leary found herself in the family reunion and potluck planning roundelay of a famous actress she barely knew. (This happens occasionally; Ann’s husband is the comedian and actor Denis Leary.)

A beauty known for playing chief executive officers, presidents and other powerful women, the actress turned out to be something of a General Patton in real life, too. “Aren’t potlucks supposed to be casual, bring-what-you-want affairs?” Ms. Leary asked. “This woman was telling everyone what to bring in the most minute detail. Like: ‘You bring the feta and red bell pepper pasta. I’ll bring loose sea salt. Tell Peter to bring the pepper grinder. Will we have enough candles? Who will bring the matches?’

“Not knowing who anyone was, at first I responded, ‘Hey, sounds yummy, but seriously, I don’t think I belong in this email group.’ But there were so many emails back and forth that they didn’t notice or acknowledge me.” Finally, Ms. Leary gave up and started chiming in with possible contributions: “I’ll bring my famous banana bread!”

“After three days the actress realized what had happened and was like, ‘Ann?’ ” Ms. Leary said.

At least Ms. Leary ended up on an endless email chain that comprised two of my favorite things: celebrity and food. I share the same name and very similar email with a woman whose life is a never-ending series of excited! emails! from her personal shopper, Phi Mu Alpha sisters and knitting club. That was fine.

Then I started receiving emails from friends who had irrefutable proof that President Obama was born in Kenya, learning socialism at the dusty feet of his tribal overlords. One day I couldn’t take it anymore, and hit “Reply All” with my thoughts. The liberal pantywaist was removed from the thread.

So what are people to do when they have made a huge honking auto-fill error? First, take heart: If you are using some email programs, like Gmail, you can take back your email within the first 30 seconds of sending, according to a Google spokeswoman. To enable this feature, follow the directions for the “Undo Send” lab.

What if you recognize the error of your ways after, say, 31 seconds? I have had those moments of slow-mo horror, where I simultaneously realize my mistake, smash my keyboard and try to concoct the most plausible lie possible, while hyperventilating at my desk.

“When email gets you into trouble, don’t use email to try to get yourself out of trouble,” said Will Schwalbe, the Internet etiquette expert and author, with David Shipley, of “Send: Why People Email So Badly and How to Do It Better.” “You can start the apology on email, but you need to continue it with a call, a letter, flowers, wine, whatever it takes. The bigger the faux pas, the more dramatic the gesture. Email apologies (even for email errors) are like email thank yous: great for speed but ultimately not very impressive.”

Yet there can be an upside to the inadvertent blurt because, for all the embarrassments, there are those moments of inadvertent connection; you may well end up stumbling over not just an old enemy, but an old friend.

One of my closest buddies and I had an enormous fight several years ago. I believed I was the wronged party, but in fact I wasn’t. Yet I was too proud, and too hurt, to make amends. A few weeks ago, in sending out a group email for a get-together, I mistakenly included her address. She wrote back, saying that although she knew she was not supposed to be on this chain, she was glad I messed up, because she missed me.

After five years’ absence, we’re seeing each other next week. I kind of love my auto-fill.