Iterable, a marketing solution for B2C companies, announced today a funding round of $23 million led by Index Ventures.

The San Francisco startup offers companies a multi-channel solution to interact with their consumers according to their behavior via email, mobile push notifications, SMS, and, most recently, in-app messaging.

“I think it’s a common problem when you’re in marketing that you always want to do more, and there’s just nobody there to help you get the right data or the right logic into place,” cofounder and CEO Justin Zhu told VentureBeat in an interview. “So we really empower the marketer to be as effective as the engineer in terms of creating campaigns and spreading them on multiple channels.” Zhu is a former software engineer at Twitter, where he helped build notification platforms on the User Growth and API teams.

Iterable is taking on the likes of MailChimp, which also serves marketing purposes. However, Zhu pointed to the fact that MailChimp’s service is email only and targets a smaller database of users. “We typically target companies that have at least 200,000+ contacts,” Zhu said. “MailChimp is efficient for newsletters, but as you get bigger, you really want to do onboarding series and have a mobile app where you can do push notifications or SMS.”

Iterable sells software as a service (SaaS) to companies based on the number of contacts they have. The monthly fee starts at $2,000. The startup has over 70 customers, including Yelp, which uses the service for newsletters (content and coupons) and ongoing lifecycle campaigns that segment the new customers from the recurring ones. Zillow is also a customer, using the service for all marketing communications, but also for transactional purposes.

When asked whether the multitude of communication channels developed to interact with consumers is too invasive, Zhu responded, “That’s a big concern for our marketers, because if you overset pushes, then consumers are just going to disable the notifications or uninstall the app.”

The service therefore provides additional information to marketers, who can then tailor their outreach according to consumer behavior. If consumers are opening every email, clicking on links, and responding to in-app messages, then marketers know that they are engaging. “We take the data not only from the emails but also from the company’s website and mobile app so that we can determine the right channel,” Zhu said.

Iterable has raised over $30 million since it was founded in 2013, and it will use the new money to further growth via hiring, sales, and marketing. CRV and AngelPad also joined the round. Iterable currently has 36 employees.

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