This article first appeared on Slate.

Email signatures, like the people who craft them, come in many molds. Some are pithy and professional, bordering on brusque. Others are quirky, incorporating tildes, fuchsia-colored fonts, and motivational platitudes. Too many are overdone, an explosion of links, websites, and, cruelly, fax numbers.

But one item is a curious constant of email signatures: the sender's email address. It's an inexplicable, redundant practice. In nearly all email clients and browser-based inboxes, simply hovering the mouse over the sender's name shows the address, unless it's already displayed. Plus, you don't need to grab an email address from someone's signature to write back. You can just hit reply.

How annoying are email addresses in email signatures? Imagine a nondigital analogy: It's like placing two return address stickers on an envelope. Or, at a party, reintroducing yourself after the host has already done so.

"Mary, this is Kevin."

"Hi, Mary. My name is Kevin."

And yet most of us are guilty. Check your own signature box: There's your email address just beneath your name, hyperlinked and lingering perfunctorily.

I first assumed there was a reason beyond my understanding. Do we include our email addresses for inbox SEO purposes? To provide clarity when a frequently forwarded missive becomes unwieldy? Perhaps it's a courtesy for those Luddites who prefer to print their emails and read them as ink on paper.

Surprisingly, there's no email-signature scripture that provides an authoritative explanation. Gmail's signature tutorial is thorough, but offers no ruling on including an email address. (It's worth noting, however, that Gmail's sample signature doesn't do so. It reads: "Elena Montevista / University of California, Berkeley.)

A wikiHow treatise stresses the importance of including an email address--but shares no explanation. A brief write-up on a human-resources blog offers the most compelling rationale: to make it unequivocally, overwhelmingly easy for recruiters and clients to contact you.

Linda Gallant, an associate professor of communications at Emerson College in Boston, says this repetition isn't necessarily a bad thing. "Redundancy can be a very good process in an age of information overload," she says. "You want people to know where to find your information without thinking about it." Further, Gallant says signatures play a paramount role in the email world: They're digital business cards that should contain all your important contact information.

But other experts view this email signature practice as antiquated, a vestige from the days of stamps and letter openers.

"I think it's a hangover from email's analog antecedent," said Jeff Ritchie, an associate professor of digital communications at Lebanon Valley College in Annville, Pennsylvania. "People are applying this metaphor of mail to email in an attempt to understand it." Ritchie's own email signature includes his title and phone number--but no email address.

"We base our understanding of the new through the lens of the old," Ritchie adds, noting our tendency to call a computer's home screen a "desktop." Or, in the early 20th century, our inclination to dub cars "horseless carriages."

Vincent Raynauld is Gallant's colleague at Emerson, and specializes in communications and social media. But like Ritchie, Raynauld says the practice is an artifact. "It shows a disconnect between social norms and technology," he said, likening the inclusion of an email address in a signature to signing one's name to a Facebook missive. And our changing technological habits may spell the end of the overstuffed email signature before etiquette does: As the time we spend online increasingly shifts to smartphones and tablets, more and more of postscripts simply read "Sent from my iPhone" or something similarly pithy. Often, mobile users drop signatures altogether--which might signal not just the extinction of the particularly aggravating habit of including an email address in a signature, but signatures altogether.

If there is a final authority on email signatures, it might be Ron Cates, the director of digital marketing education for Constant Contact, the ubiquitous email service. Cates is uncompromising in his opinion: "I think it's a bad idea."

"More than half [of] people are reading their email on their phone," he added. "Very few people make it to the bottom [of messages]--having a really long email signature is silly." Cates' signature is appropriately efficient: His company, his title, and his Twitter handle.

For a better understanding of just who participates in this nonsensical practice, I carried out an unscientific survey, quizzing folks from a variety of industries. Perhaps it would provide enlightenment: Is this a right-brain or left-brain trait? Something unique to the digitally savvy or unsavvy? My findings:

The computer programmer. Kirk Is of Massachusetts abstains, but has a few theories on why others partake. "They might be trying to point out their most canonical or reliable contact address," he says. It's not nearly as puzzling as when folks include a physical address, he adds. "Rarely have I had the urge to say, 'let's take this exchange to snail mail.'"

The educator. Exa von Alt is an administrator at a private school in Dallas and a former public school teacher. Her work-email signature includes her email address, but not for a specific reason. "We include our email addresses in our email signatures because of inertia or compliance," she says, noting some employers mandate a specific signature format. In her personal email, it's absent.

The marketer and the fashion designer. Marketing manager Megan Stalnaker of New York City indulges. "I'm branding myself," she says. But her husband Joseph, a fashion designer, is vehemently anti-. "It's redundant," he said. "I also don't like to see someone's job title. I think it's pretentious."

The firefighter. Kyle DeMaster, a Long Islander, doesn't spend his workdays tethered to a keyboard. Not surprisingly, he says just a name works fine in the signature field--no embellishment necessary.

The custom seems to obey no logic: It can be parsed neither by profession nor state. But maybe we shouldn't fret about this particular quirk--there are far worse email signature sins, says Jacqueline Whitmore, a business etiquette expert in Palm Beach, Florida. Whitmore has witnessed deplorable signatures: Horrors composed of emoticons and religious passages, bizarre fonts, and blinding colors.

"Some people haven't been trained in how to write a professional email," Whitmore says. Perhaps the death of the email signature couldn't come soon enough.