Backend Engineer (MTA), Core Sending

Resend is growing fast, and there are now over 2 million developers using it. As the Core Sending Squad, we are responsible for building and maintaining the core components of Resend that handle sending transactional and marketing emails. This role is fully remote-based in Americas or European time zones, with some expected travel for team off-sites, conferences, meetups, and more. Read more about how we work, how we hire, and what we value here https://resend.com/handbook. 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,...