In Houston, the Amaya family has spent the last few days waiting by the door for UPS to arrive. But after 10 days and two delays, they had just about lost hope. KPRC-TV's Gianna Caserta reports.

The Grinch has company.

Thousands of Americans awoke to find that special something missing from beneath the Christmas tree Wednesday, a day after UPS acknowledged getting swamped by the seasonal cheer and failing to deliver orders in time.

Now, rival FedEx appears to share the blame for the holiday that wasn't.

"We're sorry that there could be delays and we're contacting affected customers who have shipments available for pickup," Scott Fiedler, a spokesman for FedEx, told the Associated Press Wednesday.

Pressed Christmas afternoon, a supervisor at 1-800-GoFedex, the customer support line, went further in a call with NBC News. He declined to give his last name, citing company policy, but acknowledged “extraordinary” delays at the shipping giant and said his team had been apologizing to customers.

"We give our apologies to customers," he told NBC News, noting that bad weather had crippled planes and delivery trucks and unforeseen demand swamped what vehicles remained in operation.

That mirrors what UPS first acknowledged on Tuesday, as the complaints piled up and packages failed to arrive.

"The volume of air packages in our system exceeded the capacity in our network," UPS spokeswoman Natalie Godwin said in a statement.

And less-than-jolly customers of both companies took online to pummel the shipping giants.

"UPS SUCKS," wrote Kip Ingram in a post on the company’s Facebook page, just a short scroll from a "Happy Christmas" message from the company’s delivery crew. "They just FAILED. SUCK, SUCK, SUCK!"

"Merry Christmas FedEx," wrote Teri Martin in Phoenix, Arizona. "Thanks for taking my money, ruining my son's Christmas and taking days off to avoid dealing with desperate customers trying to find out how to get their packages! NEVER AGAIN!!!"

"I. WILL. NEVER. USE. UPS. AGAIN!" vowed Judie Larson on Twitter, which fluoresced with messages bearing the hashtag "#UPSfail."

For some, the void under the tree came despite days of phone-and-Web wrangling with UPS customer service. In Houston, the Amaya family toggled between tracking their package online and waiting by the door for UPS to arrive. But after 10 days and two delays, they finally gave up hope.

"My kids and the rest of my extended family have no presents," a deflated Jill Amaya told NBC News.

Christmas is about more than just stuff, many posters acknowledged, but even some of the smaller, more symbolic gifts of Christmas got lost in transit.

Samantha Edussuriya, the director of online content at Fuse.tv, the music website, took to “social media shaming” after FedEx failed to deliver her mother’s passport in time for a family trip to Mexico.

The document was supposed to arrive in San Diego by Tuesday, she told NBC News, but instead the family tracked the package through Texas and Indiana. Even after it was marked “en route” it appeared not to be moving—and as of today it still hasn’t arrived.

"Everyone was gushing with guarantees on Sunday when we asked FedEx if they could handle the order," says Edussuriya. "Now my mother is alone in San Diego and in tears."

Katherine McEachen of Fairfield, Conn., suffers from lupus and complications left her bedridden much of the fall, when she leaned heavily on her father for help. She recovered by the holidays and the family cut down a tree together, a moment McEachen recorded with a photo she arranged to have put on a mug and shipped to her father, beneath the message, “I love you”— a message that has yet to arrive.

"UPS ruined my Christmas," McEachen told NBC. “It's just a mug, but it was supposed to be so special and it's the only way I can say those words to him."

"Can UPS Save Christmas?" reads an unfortunately timed headline on the cover of the current edition of Bloomberg Businessweek, which went out to the magazine’s one million subscribers.

The answer, evidently, was "no."

"UPS understands the importance of your holiday shipments," the company said in a Christmas Day statement on its website. "However, the volume of air packages in our system exceeded the capacity of our network immediately preceding Christmas so some shipments were delayed."

Amazon.com, one of the country’s biggest package shippers, also cited UPS’s “failure” in an apologetic email to customers on Christmas morning.

In addition to reviewing the performance of delivery carriers, Amazon spokesperson Mary Osako confirmed that Amazon is also attempting to placate affected customers by providing gift cards and refunds for shipping charges.

UPS itself is on a condolences tour, telling NBC News in a statement that only “a small percentage” of packages were affected and pledging that most of these will arrive by Thursday.

The last time a significant number of UPS packages were late for Christmas was 2004, when an ice storm crippled Worldport, the UPS distribution center in Louisville, Ky., in the run up to the holiday. Back then employees ended up manually loading packages for days, and surprising revelers with Christmas Day deliveries. This year the company declined to call its workers in for holiday service.

It’s still unclear where the UPS network broke down, and the company has declined to specify the size of the problem. But Bloomberg Businessweek published just this week detailed the challenges likely to have stymied Santa’s corporate helper this year — and spotlighted the man who may take a fall for the year’s mishaps.

Scott Abell is known as “Mr. Peak” to the brown-shirted faithful, and he spends his whole work year outlining the company’s holiday delivery plans, scrambling hundreds of planes and thousands of trucks from his office at Worldport.

Beyond icy weather, which hampered the UPS and FedEx distribution hubs, the companies were likely squeezed by a smaller window for holiday shopping and a record number of e-purchases being pushed through at the last minute. There were just 26 days between Thanksgiving and Christmas

At the same time, there was the continued growth of online shopping, which not only facilitates last-minute gifting but often rewards it with deeper discounts.

Online spending jumped 9 percent, to $37.8 billion, between Nov. 1 and Dec. 15, according to the online research firm comScore, and retailers expect overall holiday sales to be up nearly 4 percent, exceeding $600 million.

UPS anticipated delivering 132 million bundles in the week before Christmas, according to Bloomberg Businessweek, and to meet that wave of holiday cheer, Abell organized 55,000 part time workers, 23 extra planes and what amounts to a second fleet of delivery trucks.

Between Thanksgiving and Christmas, FedEx handled 275 million shipments, Fiedler, the UPS spokesman, told the AP. Those that were not delivered in time, he said, "would be very few."

A last-minute decision by one of UPS’s clients — reportedly Amazon.com — dumped additional packages into the system last weekend, but Abell doubled the number of shifts at Worldport, still hoping to stay ahead. It wasn’t enough.

Abell usually heads to Florida in January to play golf and decompress after the madness of the holidays. When he returns, the 31-year veteran of the company gathers his lieutenants for a special lemon session, detailing all that could have gone better in the weeks before.

Already he’s taken a small personal step to alleviate his workload, telling his immediate family to go easy on the online shopping. “I tell them that they should do it early,” he said, according to his magazine profile. "Early’s better."

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