It's almost a startup Cinderella story: two college acquaintances reconnect after graduation and take a risk on a business that turns out to be a wild success. Danielle Weisberg and Carly Zakin bonded while interning at NBC, and the self-described "news nerds" discovered that for people whose job doesn't require much knowledge of what's going on in the world, current events knowledge tends to fall to the wayside.

To combat this issue, the friends built theSkimm, an email that arrives in your inbox every morning with a brief digest of that day's headlines. The business model has proven successful, with 1.5 million happy subscribers.

Here are some factors to theSkimm's success:

#1: Use Your Own Voice

The news digest provided by theSkimm isn't the same news you'd read in the paper; it's the news as told to you by a smart, savvy friend. The business was started with young, professional women in mind, and the voice of the brand has captured that audience. The conversational tone of theSkimm and its inclusion of pop culture news and viral Internet trends make it relatable.

#2: Know Your Audience

Weisberg and Zakin tailored their business format around the lifestyle of their audience. They knew that busy professionals often check their email first thing in the morning, and so an email newsletter was the natural choice to get their attention. Fitting into an already established routine makes a service much easier to adopt.

#3: Stick to Your Guns

Both founders have demonstrated extraordinary tenacity in the founding of this business, as they quit their jobs to do so, even when many people were telling them "email is dead." However, Weisberg and Zakin were confident that they could market to other busy professionals who still value email like they do.

#4: Do What Feels Natural

Both Weisberg and Zakin have stated that they had always filled the role of relatable informants among their friends. As Weisberg said to Gotham Magazine, "The idea was the easy part. It was taking the role--dishing about the news with the right bit of snark-- that we had always played for our friends and turning it into a business."

#5: Stay Involved

When a brand has reached Oprah-level recognition like theSkimm has, you would assume that the founders would have handed off all the writing work to employees. That's not the case, according to Weisberg and Zakin, who have stated, "We still touch every word." It's the duo's signature voice that keeps subscribers interested, and they understand the importance of their involvement in the copy. Signature section headings like "The Story" and "The Why" allow readers to find what they want to know, and to understand it without reading thousands of words. The "smart friend" voice is what makes theSkimm so approachable.

#6: Embrace Word of Mouth

One of the secrets of theSkimm's astronomical growth is its referral program. Five weeks after a user signs up with the service, they get an email asking them to share their unique Skimm URL with ten friends. If the ten friends join, the user becomes a "Skimm'bassador," a job that comes with perks like party invites and daily opportunities to win prizes like totes and sunglasses. TheSkimm attributes 10% of its signups to their 6,000 Skimm'bassadors.

Daily emails are not a new business model by any means, but the founders of theSkimm managed to breathe new life into a communication tool that many businesses have written off as tired or ineffective. By sticking to a clear demographic, and speaking to them in terms they understand, theSkimm has found a way to revitalize both email newsletters and the news for a hip, young audience.