Backend Engineer, MTA

Resend; Ireland; Remote; EUR 110,000 - 150,000; Full time

Job summary

Resend is hiring for a backend-focused role to build and operate its email transport infrastructure. You will work on SMTP delivery, MTAs, routing, retries, and throttling to ensure reliable, scalable email sending.

You will implement systems for IP pools, warmups, and reputation-aware routing while improving bounce/deferral handling and observability. The role emphasizes ownership, reliability, and deep collaboration with Trust & Safety and Core Sending to safeguard the sending network.

Qualifications

• Strong backend engineering experience required.
• Experience with high-volume delivery systems or messaging infrastructure desired.
• Understanding of queues, retries, idempotency, rate limits, backpressure in distributed systems.
• Experience or strong interest in SMTP, MTAs, DNS, bounces, deferrals, IP pools, mailbox-provider behavior.

Responsibilities

• 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 to 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 and Core Sending to build controls protecting the sending network from abuse.
• Participate in incident response for sending, provider, and deliverability-sensitive issues.
• Be on-call for critical services.

Skills

Backend engineering

Email infrastructure

Distributed systems

SMTP & MTAs

DNS & IP pools

Observability

Reliability

Job description

Resend is building the most accessible email platform for developers. As we’ve grown to 4M+ users and continue to onboard thousands of new users every day, the pressure of maintaining a safe place for good senders continues to build. 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 .

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 and Core Sending 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 syst