Senior Software Engineer - Email Channel

Customer.io is a platform used by over 8,000 companies to power automated communication. They are looking for experienced engineers to own the email channel end to end, focusing on both frontend experiences and backend systems that support high-volume email sending.

Responsibilities:

• 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

Requirements:

• 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