Backend Engineer , Core Sending

As a Backend Engineer on the Core Sending Squad, you will build and operate Resend’s email transport infrastructure, focusing on SMTP delivery, MTA systems, and routing. You will design systems for throttling, IP pools, and reputation-aware routing, and improve bounce classification.

About the job

In this role, you will…

Build and operate Resend’s email transport infrastructure
Work on SMTP delivery, MTA systems, routing, retries, backoff strategies, and delivery controls
Design systems for domain-level, provider-level, customer-level, and IP-level throttling
Build infrastructure for shared IP pools, dedicated IPs, warmup execution, and reputation-aware routing
Improve how Resend classifies bounces, deferrals, transient failures, hard failures, and delivery outcomes
Build tools that help the team debug delivery issues by customer, domain, mailbox provider, route, IP, message type, and event
Help design systems that make sending behavior safer, more observable, and easier to operate
Translate reputation strategy into backend systems
Partner with Trust & Safety to build controls that protect Resend’s sending network from abuse
Participate in incident response for sending, provider, and deliverability-sensitive issues
Be on-call for critical services

You will be a great fit if you...

Have strong backend engineering experience
Have worked on email, messaging, notifications, communications, infrastructure, or other high-volume delivery systems
Understand queues, workers, retries, idempotency, rate limits, backpressure, and distributed systems
Have experience or strong interest in SMTP, MTAs, DNS, bounces, deferrals, DNS, IP pools, and mailbox-provider behavior
Care about reliability, observability, operational excellence, and reducing blast radius
Have low ego, high ownership, and strong taste for simple systems