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 the email 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 channels in the industry.

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.

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.

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

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

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.

• →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

• 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

No gotchas, no trick questions — just a clear, human process designed to help both of us make an informed decision.

• Application — We review everyone with care. Tell us why you're interested.
• Recruiter Call (30 mins) — Let's chat about what you're looking for and how we work.
• Behavioral Interview (60 mins) — Talk with one of our hiring managers about your experience, values, and working style. We'll explore topics like ownership, product thinking, and collaboration.
• Technical Interview (60 mins) — A collaborative system design conversation focused on scaling challenges.
• Take-Home Assignment — Complete a short, realistic task similar to what you'd work on here.
• Assignment Review Call (60 mins) — Walk us through your work and discuss tradeoffs, priorities, and how you'd iterate.
• Project Deep Dive (60 minutes: A focused conversation on a technical project you've owned end-to-end, and how you balance planned work against urgent, customer-impacting issues.

All final candidates will be asked to complete a background check and employment verifications as part of our pre-employment process.

Customer.io recognizes the stifling impact of systemic injustice on diverse communities. We commit to using our influence to increase inclusion and equity within the tech industry. We strive to build an inclusive team culture, implement bias-free hiring practices, and develop community partnerships to expand our global impact.

Zoom is the only video conference platform that we use, virtual interviews will be conducted using the video capability (i.e., not via the chat), and offers will be extended in writing on official Customer.io letterhead. Please be vigilant in all of your job search activity, and if you have any questions please contact jobs@customer.io.

We believe in empathy, transparency, responsibility, and, yes, a little awkwardness. If you're excited by what you read and want to build software that makes communication better for everyone — apply now.