Senior Software Engineer - Email Channel

Hi, I'm Brian, Senior Director of Engineering at Customer.io. We're looking for experienced engineers who want to own a channel end to end — from the infrastructure that delivers billions of messages reliably, to the product surfaces our customers use to build, send, and analyze their campaigns. You'll work across the stack, bringing both systems thinking and product craft to one of the most technically rich problem spaces in the industry.

You don't need email experience to apply.

We can teach you the email domain. The engineers who thrive here are the ones who love learning a deep problem space, not only the ones who arrive already knowing it.

About Customer.io

Over 9,000 companies — from scrappy startups to global brands — use our platform to send billions of emails, push notifications, in-app messages, and SMS every day. Customer.io powers automated communication that people actually want to receive.

We help teams send smarter, more relevant messages using real-time behavioral data. Under the hood: Go, React, Ember and AI help us ship fast and scale with confidence.

What We Value

Ownership

You own problems end to end. You move fast, act like an owner, and thrive in ambiguity. You've led complex projects before, whether officially or not, and you're ready to do it again.

Engineers with product taste

You think like a user, not just an engineer. You care how your systems power real customer value — and how to make them better.

A healthy skepticism for "the way things are done"

You bring rigor and creativity. Best practices matter — but never more than forward motion.

What You'll Do

• Build and evolve the frontend experiences customers use to create, preview, and analyze campaigns — editors, configuration, and analytics dashboards
• Design and scale backend systems that process high volumes of messages and events: queue management, retry logic, rate limiting, and real-time event pipelines
• Build automated systems that respond intelligently to feedback signals from external providers — classification, suppression, throttling, and health scoring
• Partner with in-house domain experts to turn their knowledge into automated tooling — you bring the systems skills, they bring the email depth
• Instrument and monitor channel health end to end: signal detection, anomaly alerting, and observability
• Own problems end to end — from architecture and schema design to testing, deployment, and monitoring
• Participate in an on-call rotation as required, supporting the reliability of the systems you build
• Share knowledge and raise the bar through short videos, thoughtful writing, and mentorship
• Use AI agents to make multi-file changes by scoping the work, writing the prompt, and verifying the output

What We're Looking For

• 7+ years of experience building scalable, distributed systems in Go (or similar statically typed languages)
• Experience building product-facing frontend features in React or similar frameworks, with attention to UX quality and polish
• Experience building or consuming APIs that handle high-throughput async workloads — event streams, queues, and systems that degrade gracefully under load
• Comfort integrating with external systems you don't control — third-party APIs, rate limits, opaque failure modes — and designing for resilience around them
• Comfort working in cloud-native environments (AWS, GCP)
• Familiarity with relational databases (we use MySQL primarily) and an understanding of performance tradeoffs
• Experience with observability tooling and operating production systems
• A bias for action over perfection, and pride in owning technical decisions
• Nice to have: Familiarity with email infrastructure — deliverability, authentication standards (SPF/DKIM/DMARC), sender reputation, or high-volume sending