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Scaling, Personalization & Liquid Language with Customer.io

“Customer.io is a great tool. It’s awesome for managing emails, and for creating personalized emails, thanks to its Liquid language support.”

-Matthieu Vaxelaire, CEO ofMention

Some tools stick out from the bunch. That’s how we discoveredCustomer.io, which was used by about a dozen different startups we’ve talked to, including Segment and TripleMint. While Customer.io might be used by fewer startups than the industry giants, like MailChimp, it offers more features that make it a compelling tool as companies scale their marketing. Founders love it and have recommended it to us time and time again.

“We’ve always been about helping businesses communicate with customers. Everything we do is customer centric.”

-Colin Nederkoorn, Founder and CEO of Customer.io

Customer.io is uniquely able to bridge the email marketing needs of startups who are leaving their early stages and scaling up their marketing needs. Customer.io positions itself between a simpler email marketer that get the job done, like MailChimp, and a heavy marketing suite, like Marketo. “We’re in the middle” says Nederkoorn. Most companies that use Customer.io have already raised their series A and have somewhere between 10 and 50 employees.

Customer.io is an incredibly powerful tool that takes email marketing and transactional emails to the next level. While Customer.io accomplishes the feats of similar marketing tools, such as A/B testing and landing pages, where it really stands out is in its transactional capabilities and Customer.io action.

With huge capabilities in segmentation and qualifying identifiers for transactional engagement, you can adeptly move through custom workflows, engaging customers at all stages of your startup’s conversion or sales process. This enables you to fine tune your targeting and personalize your leads, increasing the likelihood of turning a lead into a customer.

The recently launched Customer.io Actions allows users to connect any product with a public API to send messages “from push to postcards.” Among the many integrations are TwilioClose.io and, Stacklisters Lob, and Zapier.  “All this customer-centric focus is enabling you to have better communication with customers across email now.”

When to use Customer.io 

“In the early days, we were working with very early stage companies with 5 people on their team. Now, typically, we are working with user bases in the millions.”


In the years since it launched, Customer.io’s user profile has evolved along with the company itself. Though they worked with smaller teams in the beginning, their target user now has now advanced to companies that have largely grown past the early stages into larger companies with larger subscriber bases.

“Those using Customer.io most successfully are tuning it all the time, using data to tune what they’re doing and trying new things.”


Customer.io is a powerful tool that needs to be handled by an employee dedicated to the software. According to Nederkoorn, an ideal team using Customer.io would have 10-50 people working on that particular product. Customer.io generally requires a dedicated manager to get the most out of it. It is so complex and has so many nuances that it really takes a dedicated staffer to manage it. Customer.io might not be best for you if your team doesn’t have the bandwidth to support it and make the most of its powerful capabilities.

Beyond needing the bandwidth, you need to be heavily using email marketing in your outreach strategy. You also need a list big enough warranting the software. Customer.io clients with subscriber bases exceeding 500k are in a much stronger position to reap the benefits of the platform vs. companies that are just getting their email marketing off the ground.

“It’s strategic to implement Customer.io at the point where you’ve proven the product. There’s something real there, and you’re planning on building something for the long haul.”


Customer.io is a long-term investment. It’s not a good choice when you’re looking for a quick fix. However, if you are looking to build out a robust email marketing campaign to generate leads or if email marketing is your primary way of interacting with customers, then Customer.io could be the solution you’re looking for.

Making Emails More Targeted 

Customer.io started 4 years ago in New York City. Customer.io was originally created to solve a problem that Colin Nederkoorn had noticed while working for an early stage Internet company.

“The opportunity we saw was … that there was a disconnect between engineering and marketing – primarily between project managers and product marketers.”


The problem? Traditionally, there was a wall between what marketers could do and what engineers could do. To change the email or email structure required editing code and redeploying the application, which is a huge pain and prohibitive. Customer.io sought to change this and make email marketing as simple for product marketers as possible.

“The first version focused on onboarding and conversion with data coming from the app. It was much easier for project managers and product marketers to change content messages, the rules, and change the cadence of what they were sending.”


Marketers were finally able to alter the rules specs sending messages – including the audience to whom they were sending. This segmentation used effectively greatly increases the impact of your email campaigns. The ability of regular product marketers to fix their messages removes a giant roadblock from effective marketing.

Some Advice to Startups on Email Marketing

Nederkoorn has lived and breathed email marketing since he launched the company. So, in closing, we asked him to share some advice for other entrepreneurs about just that.

“Something that works for us and works for a lot of people that we’ve seen is to teach using the experience that you’re gaining… Most companies don’t invest enough into themselves to write and articulate their thoughts. This is super important as an early stage founder and company.”


Effective email marketing is about teaching your customer about your industry and about your product. If your customer is learning, they’re engaging. Becoming an authority on your subject is a great way to build your brand.

Once you’re seen as knowledgeable, people will keep coming back to you for more. Email marketing is an effective way of disseminating this information and keeping your brand relevant and fruitful.

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