BELFAST, Maine — Deep inside the Athena Operations Lodge, a massive, complicated machine gulps up envelopes, slices them open and extracts, scans and deposits the checks inside almost faster than the eye can process.

The machine, brand-new to the Belfast employees of the health care technology company, is helping them process 1.5 million checks a month. And its new home, a former warehouse built by credit card giant MBNA in 2000, has been renovated into a light-filled, spacious facility on the athenahealth campus. The lodge — complete with a stone fireplace — was built because the company’s nearly 900 employees have outgrown their original four buildings.

Officials said Wednesday at the structure’s grand opening that it will hold as many as 400 employees and that it will serve as the operations headquarters for the whole company, which is based in Watertown, Massachusetts.

“Eight years ago, we came here with this ambitious idea that would employ 800 people,” David Tassoni, senior vice president of operations for athenahealth, said at the event. “We’ve done that … Here is a warehouse that has been turned into a 60,000 square foot facility, making it possible for us to grow. I guarantee this is the most incredible remittance processing facility in the world, and it’s the headquarters for our flagship product.”

He said that the company, which has been on a long spree of renovating, building and hiring in Belfast, will be done growing in midcoast Maine once they reach 1,200 employees.

One of those employees, Megan Laite of Lincolnville, has worked at athenahealth since 2009 and is now a supervisor in the remittance and print operations department. She showed off the OPEX Eagle mail processing machine, which she said can do the work of three machines and 35 man hours on a Monday, the busiest day for mail processing, in just four and a half hours.

“We’re very excited,” she said of the fancy machine and also of the new building. “It’s so amazing to have such a great company just seven minutes from home. You just feel that sense of excitement for what we’re doing for our clients.”

Belfast Mayor Walter Ash, who attended the grand opening celebration, said he’s thrilled that the company has made such a substantial commitment to the city.

“I’m all about jobs, and I see good jobs,” he said, gesturing around the new space. “It’s a beautiful facility they’ve created here out of an old warehouse, and they’re doing what I like — employing people. I just hope they can find enough people to fill the positions.”