Senior Software Engineer - Email Channel

About Customerio

Over 8,000 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.

Channel depth

You understand the email ecosystem: how messages are routed, authenticated, delivered, and measured. You bring that knowledge into both your backend architecture and the product experiences you build on top of it.

What You'll Do

• Build and evolve the frontend experiences customers use to create, preview, and analyze email campaigns — template editors, sending configuration, deliverability dashboards
• Design and scale the backend systems that power high-volume email sending, including queue management, retry logic, and event processing (bounces, complaints, deferrals)
• Own deliverability-adjacent systems: bounce classification, suppression management, IP/domain reputation monitoring, and feedback loop processing
• Partner with our deliverability team to translate domain expertise into automated tooling — reputation scoring, warm-up schedules, sending throttles
• Instrument and monitor the health of the email channel: inbox placement signals, block detection, ESP feedback, and alerting
• Own problems end to end — from architecture and schema design to testing, deployment, and monitoring
• 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
• Comfort working in cloud-native environments (AWS, GCP)
• Familiarity with relational databases (we use MySQL primarily) and an understanding of performance tradeoffs
• Familiarity with high-volume email sending concepts: bounce handling, feedback loops, and delivery event processing
• Working knowledge of email authentication standards — SPF, DKIM, DMARC — and how they affect deliverability
• Comfortable reasoning about sender reputation, IP warm-up, and ISP behavior at scale
• Experience with observability tooling and operating production systems
• Experience building or consuming APIs that handle high-throughput async workloads
• A bias for action over perfection, and pride in owning technical decisions