Signing on as the first advertiser on "Serial" has turned out nicely for MailChimp. The podcast, which investigates the 1999 murder of a Baltimore high school student, quickly became a hit. But as its only launch partner, MailChimp's payment was calculated using an audience estimate that turned out to be a fraction of the more than 31 million downloads "Serial" has registered so far. The exposure took MailChimp's ad viral, turning "Mail-Kimp" -- the way a kid pronounces MailChimp's name in the ad -- into a social media sensation. The ad even has its own remix.

"Serial" is now being flooded with advertiser calls, and the podcast is self sustaining, a significant accomplishment for what was simply an experiment a few months ago.

Ad Age caught up with "This American Life" director of operations Seth Lind, who manages sponsorships ("Serial" is a "This American Life" spinoff), to chat about the business of "Serial" and how that MailChimp ad came to be. The conversation has been edited for brevity and clarity.

Ad Age: The MailChimp ad is a cult hit. It even gets parodied in "Serial" parodies. What's so endearing about it?

Seth Lind: In the public radio world, that kind of montage has a name, it's called a vox. People say, "Oh, let's do a vox" where you have people answering the same question, and you do a montage of their answers. So, it certainly sounds different than most single voiced podcast ads. The ad is really based around that one person not knowing how to pronounce "Chimp," and then, for whatever reason, people glommed onto it and it became a meme. That's not something you can do on purpose.

Ad Age: MailChimp got a pretty good deal given the amount of publicity the spot has generated.

Mr. Lind: Yeah, I suppose it's the type of publicity you try to hire a bunch of publicists to get and never get. They owe a big thank you to a random tourist with English as a second language who didn't know how to pronounce Chimp.

Ad Age: Wait, they grabbed people off the street to voice the ad?

Mr. Lind: Yes. It's pretty common in public radio to go out and interview people on a subject. But yeah, ["Serial" producer] Dana Chivvis just said "Do you want to voice an ad for a new podcast?" She went went out and recorded those in a day, probably like an hour.

Ad Age: So the edit team is the one that produced the ad?

Mr. Lind: Yes.

Ad Age: Are you concerned there are lines that might be blurred between edit and advertising?

Mr. Lind: We have a strict firewall between advertising and editorial in terms of content. Occasionally, a sponsor will reach out and say, 'We have a product that's this or a campaign that's this. Do you have any stories coming up about the topic?' And we're just like, 'That's never going to happen.' We're never going to associate an ad with a particular piece of content. You're sponsoring the show and you're sponsoring whatever happens to be in the show that week. ... I think it's just a point of pride to be good producers. We're producing audio that's entertaining and that ad is no different. I don't think it should be surprising that a "This American Life" or a "Serial" producer can produce an audio ad that is high quality or as good or better than something that an agency would make -- because it's actually our only job to make compelling audio.

Ad Age: Radio doesn't seem to have the same problem as print with sponsored content. Hosts, for instance, read ads all the time.

Mr. Lind: Yes, certainly in commercial radio. Sometimes, they're saying: 'You know what I love...' and you're like, 'I don't think you love that, I think you're reading a piece of paper in front of you.' But, obviously we don't do endorsements and things like that. But yes, I do think the host read spots are effective.

Ad Age: Did Chicago Public Radio make a ton of money when "Serial"'s popularity surged?

Mr. Lind: When we were conceiving of the show we went out to sponsors, and we tried to recruit them to purchase launch packages and Mailchimp did. But then once the show was popular and was getting written about, more sponsors added on. So, in that way, the visibility of it and the success of it brought in more sponsors at the tail end of the season and brought in a lot of inquiries about sponsoring in the future.

Ad Age: What percentage of the budget does advertising make up? Is "Serial" primarily reliant on ad dollars?

Mr. Lind: For the first season it was really the only revenue. Because the call for donations we did was to fund a second season. So, 100% would be the answer there. And then I would say, for the second season it's about half.

Ad Age: Podcasting is a digital format, are you able to pass along listener data to your advertisers as you would with a digital display ad?

Mr. Lind: No. We just tell them the download numbers. It's just the pure numbers. The episodes have been downloaded 31 million times, and that's across all 11 episodes. So it's just a lot of people.

Ad Age: What was the original estimation of the audience?

Mr. Lind: It's top secret. ... It was in the hundreds of thousands.

Ad Age: Last question -- did Adnan do it?

Mr. Lind: I have to admit that I do not know.