After accepting her boyfriend’s marriage proposal, Sarah Nolting, of Columbus, Ind., did what most modern brides do: She announced her engagement to her Facebook friends.

All 899 of them.

But there was room for only 250 guests at her wedding, and that meant that some of her online friends (maybe “acquaintances” would be a better term) were expecting an invitation that never arrived.

“People just assumed they would be invited,” said Nolting, 25, a communications specialist.

Before her wedding to Jonathan Nolting, 27, a construction estimator, finally arrived in October, she had fended off a colleague who had cornered her in a conference room angling for an invitation, as well as a former co-worker who had lobbied her on Facebook.

Social media is enabling the brides and grooms to share the good news of their engagement and weddings, to post pictures of parties and other mileposts along the way. But there is a downside, and not just with the large numbers of people who in a predigital age might not have known that they stand among the ranks of the uninvited.

Couples now have less control over what information is passed on about their engagement and wedding and are being confronted with a host of new etiquette questions, from when to put news of the engagement online to who gets to post the first photo from the ceremony on Instagram.

Matthew Robbins, a Manhattan-based event designer, said he had recently organized a destination wedding and that the bride felt compelled to invite 10 co-workers when her coming nuptials became a subject of discussion among them on Facebook. “She felt like she had to invite them just to acknowledge it,” said Robbins, the author of “Matthew Robbins’ Inspired Weddings.”

Not all the people who received the extra invitations accepted. And some of those who did tried to crash the couple’s rehearsal dinner and Sunday brunch.

Dana Constantino, 25, of Los Angeles, who is getting married in July to Noah Gereboff, 25, an account manager for a sales outsourcing company, came up with an alternative for some of the Facebook friends who would not make the guest list cutoff, inviting them to a rooftop engagement celebration complete with cake pops and cocktails.

“We planted the seed that it was going to be a small wedding,” said Constantino, a founder of lovedetailed.com, a site that sells wedding-related products.

For their 180-guest wedding on Long Island in June, Kim Stolz, 30, a vice president for equity derivatives at Citigroup in New York, and her wife, Lexi Stolz, 31, a wedding planner, couldn’t possibly invite all of their friends — let alone all of Kim Stolz’s 6,000 Instagram followers.

After denying invitations to roughly a half-dozen friends who “asked those leading questions,” the couple continued to encounter plenty of awkward moments.

“We’re still literally having conversations with people about why we couldn’t invite them,” said Kim Stolz, author of “Unfriending My Ex: and Other Things I’ll Never Do,” a memoir about the perils of social media.

In 2011, a Maine woman asked Peggy Post, who writes a wedding etiquette column for The New York Times, whether she should hire a security guard to deter potential wedding crashers after her newly engaged daughter had posted on Facebook, “Who wants to come to a wedding?”

Many of the daughter’s friends had responded “Yes” and had asked for directions, but the wedding was to be for 40 guests only. Post outlined precautions family members could take that would allow them to “put the Facebook ‘invitation’ out of your minds and enjoy the day.”

Contacted recently, the Maine woman, who had signed her letter Mother (aka Sentinel), recalled the episode and noted that she had posted a “reply” on her daughter’s Facebook page emphasizing that it was to be a small wedding and that those to be invited would receive a printed invitation.

“No uninvited guests appeared,” wrote the woman in an email. “I figured either her Facebook ‘friends’ either saw my warning or didn’t have a chance to see that wide-open invitation before she deleted it.” No guard was hired.

With couples sharing everything on their social media feeds, from the type of wedding cake they ordered to the bath towels on their registries, it’s no surprise that there is confusion over exactly what are the appropriate — and inappropriate — uses of social media.

“We don’t have a book of Emily Post rules,” said Anja Winikka, site director of TheKnot.com, a wedding website, adding that the online etiquette guidelines for brides and grooms are “evolving.”

For example, while many couples encourage guests to post pictures of their festivities online, creating wedding day hashtags (often a mash-up of the bride and groom’s last names), Winikka said the first photo posted of the bride should come from someone close to her, such as her maid of honor. Other guests “have the green light from there,” she said.

Lisa Gaché, the owner of Beverly Hills Manners, an etiquette consulting company, offered two other suggestions for brides and grooms:

• Refrain from posting “any details that should be privy to only the people who are invited to the wedding,” like the wedding location or the band that will be playing at the reception, because it might be construed as “exclusionary.”

• Don’t post anything that could be perceived as bragging, like the size or cost of an engagement ring, or mention the registry, which might sound as though you are fishing for gifts.

“It’s distasteful,” said Gaché, the author of “24 Karat Etiquette: Golden Rules From the World’s Most Glamorous Zip Code.”

Colin Cowie, an event designer with offices in New York and Los Angeles, said he is writing a book that will discuss social-media-related manners. On the top of his current list of offenses? Brides who post too many details about the wedding before the day of the festivities, spoiling surprises, and guests who use iPads to take pictures or film a marriage ceremony (“It steals something from what is supposed to be a sacred moment,” he said).

Friends snapping pictures during her vows annoyed Natalie Bloomingdale, 29, who was married in February in Austin, Texas, to James Bloomingdale, 31, a senior vice president at a private equity company. “There were flashes going off left and right. It was very distracting,” said Bloomingdale, a publicist in Los Angeles.

For many bride and grooms, though, social media has been no problem.

Ethan Long, 27, a copywriter for an advertising agency, has not received any Facebook messages asking for invitations to his wedding to Alexandra Calvano, 26, a registered nurse, in September in Cape May, N.J., but wouldn’t cave to pressure if he did. “If one of my friends doesn’t feel included, that’s unfortunate, but I’m more focused on the wedding than managing people’s feelings,” he said.

Besides, as Constantino put it: “People put everything on social media. Why have your wedding be something you are hiding?”