What is Customer.io?
Customer.io is a Behavioral messaging platform founded in 2012, headquartered in the United States. Starting at $100/mo, it targets product teams that trigger messaging from event streams and keep their own SMTP, Twilio and push credentials. Our verdict: One million emails included at $100, and rate limits published per API. Watch for: No free plan, a $100 floor, and billing on stored profiles. Rated 7.1/10 overall across ease of use, deliverability, and pricing value.
What is Customer.io?
Customer.io started in 2012 as an analytics product and stopped being one after about a dozen sales calls: prospects already owned analytics tools and wanted something that would act on the data instead. Colin Nederkoorn and John Allison rebuilt it as a rules engine sitting on event streams, ran the first version by hand while customers assumed it was automated, and took eighteen months to reach $10,000 in monthly recurring revenue. The company crossed $100 million in annual recurring revenue in September 2025, having raised under $4 million before its first institutional round in 2022. Roughly 2,500 of its own customers are shareholders, from a Regulation CF raise in 2021 that filled in less than a day.
The distinguishing trait is that it does not insist on being your mail server. Email can go out through your own SMTP, with documented setups for Postmark, SendGrid, Mailgun, Mailjet, Mandrill and SparkPost; SMS can run on your Twilio, Infobip, Vonage or Sinch account; push needs your own APNs and Firebase keys. A workspace can hold up to six SMTP servers routed by message type, and none of it is gated behind an enterprise contract.
Billing counts profiles, and a profile can be a company or an order as well as a person, which is part of why the entry plan starts at $100 a month. Notion, Lemonade and Buffer are customers.
Explore Customer.io on SMTPedia
Frequently asked questions
Is Customer.io worth it in 2026?
Our full editorial review covers pricing, deliverability, ease of use, support quality, and API/MCP maturity. Read the Customer.io review →
How much does Customer.io cost?
All pricing tiers, hidden fees, refund policy, and the true cost per email are broken down in the pricing tab. See Customer.io pricing →
What are the best alternatives to Customer.io?
Customer.io compared with its closest competitors by use case, pricing, and switching cost. See alternatives →
What are the SMTP settings for Customer.io?
Hostnames, ports, authentication, rate limits, and DKIM/SPF configuration for Customer.io. See SMTP settings →
Does Customer.io have an official MCP server?
Our API tab covers Customer.io's REST API version, SDKs, rate limits, and MCP server support (official, community, and commercial wrappers). See API + MCP →
This review follows our email infrastructure testing methodology. We disclose affiliate relationships in our editorial independence policy.
