Case Study: Customer.io achieves scalable, high-volume email delivery with Mailgun

Customer.io - Customer Case Study

Customer.io is an automated messaging platform that helps marketers and product teams send behavior-driven emails, onboarding flows, transactional messages and newsletters across many industries. As the company scaled and onboarded high-volume senders, their original Email Service Provider began deferring millions of time-sensitive messages and creating a poor user experience, so Customer.io needed a more reliable, high-performance ESP that wouldn’t compromise deliverability.

They migrated to Mailgun, working with a Technical Account Manager to coordinate DNS updates for 2,300+ customers and to gradually warm new IPs by routing a small percentage of traffic to Mailgun before ramping up over three weeks and completing the move in about three months. The switch delivered higher volume capacity, faster send speeds, simpler IP/domain management, improved deliverability and stronger customer trust—backed by ongoing Mailgun support and partnership.

Customer.io

John Alison

Co-Founder