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.

About Customer.io

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, dis