Brittany Howard, singer/songwriter/guitarist for Alabama Shakes, missed her appointment. It’s the kind of thing that happens when your band is blowing up, going from dumpy bars to sold-out tours, international dates and MTV in a few short months. The buzz is so infectious even the local sheriff wants in on the action, and earlier in the day he held a ceremony to make Howard an honorary sheriff’s deputy. “Funny story,” she says. “I was the only one who didn’t show up for it.”

These moves only add to the rock-star mystique of missing your own celebration, but Howard didn’t mean to blow anyone off – life is just a whirlwind for the 23-year-old, who was still carrying mail for the U.S. Postal Service as of last November,.

Formed in the small north Alabama town of Athens, the band began to take shape in high school when Howard met bassist Zac Cockrell. Before long, the duo linked up with a couple of older musicians – drummer Steve Johnson and guitarist Heath Fogg, both from the Athens High class of 2003. In 2009, Alabama Shakes was officially born. (Lately, Ben Tanner has been helping out on keys.)

Like most young bands, the quartet was struggling to find a way to make music a full-time job until one day last July when Justin Gage of indie music blog Aquarium Drunkard contacted Howard and asked if he could post one of the group’s songs on the site. She sent him “You Ain’t Alone,” a slow-burning soul number that sounds like it could have been cut 50 miles west of Athens at the famous Muscle Shoals Sound Studios.

Everything changed overnight. Prior to the Aquarium Drunkard post wasn’t anything available online or for sale and if you weren’t at one of the band’s incendiary live shows, then you simply couldn’t hear Alabama Shakes. Within weeks, the band had signed with ATO Records and High Road Touring, landed a song in a Zales diamond commercial, quit their day jobs. And now, fans of the band include Drive-By Truckers’ Patterson Hood (who took them on the road to open for the DBTs), Adele, Bon Iver, Booker T. Jones, David Byrne and Jack White, who invited the band to initiate a new live 45 series for his Third Man Records.

“Looking back over the past few months, it’s just unreal,” says Fogg. “We’ve been a band for almost three years and this time last year, we couldn’t get a gig. Now, we played these shows on the West Coast and sold out every one. It’s shocking; I don’t know how it happened.”

This April, Alabama Shakes deliver their full-length debut, Boys & Girls. Leading up to the recording sessions, the sound engineer asked the band to send him a few tracks to get a feel for what they were trying to achieve. They sent one song by The Supremes, one by Lee Fields and one by My Morning Jacket.

Howard – who people frequently compare to Aretha Franklin and Janis Joplin for her unhinged howl and bold stage presence – admits that everyone in the band loves classic R&B, but insists the retro-soul tag they’ve acquired isn’t accurate.

When asked about her influences, she lists Chuck Berry as her favorite guitarist and David Bowie as her favorite songwriter and likes to remind people that her first band was a punk act. “James Brown and Otis – that to me is basic music education. And we all have an affinity toward it and understand it, but at the same time, I love old school rock and roll,” says Howard. “I love Queen. I love Black Sabbath.”

Fogg is honored when folks refer to them as classic- or retro-soul, but, like Howard, he sees the band in the margins where genres bleed together. “A lot of rock and roll music and classic R&B – and even a lot of country music – are all so closely related we walk that fine line,” he says. The result is a group that plays rock like an R&B band and R&B like a rock band. There’s also something undeniably gospel-like deep in their roots.

Alabama Shakes is a band on the brink, poised to jump into true stardom, but the members are aware that sometimes when things burn this bright, they burn out twice as fast. Today, they don’t worry about getting people to listen; now, they’re concerned about over-exposure. They aren’t afraid to laugh at the irony and are certainly aware how lucky they are.

“I don’t actually have any expectations whatsoever,” says Howard. “Everything that’s happened is amazing: I got to see our country, I’m gonna get to go overseas, I’m gonna get to go to Europe. If it all stopped tomorrow, I’d still be pretty happy.”