Sr. Lead Software Engineer - Messaging Infrastructure

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Klaviyo is a leading marketing automation platform that helps businesses grow by delivering personalized experiences. Our mission is to empower creators to own their destiny. We believe in providing an exceptional developer experience that enables our engineering teams to build and ship high‑quality software efficiently and with confidence.

The Messaging Infra organization at Klaviyo is focused on high‑growth customer engagement through various messaging channels (email, SMS/MMS/RCS, mobile push, Whats App, and more). We work with multiple stakeholders to provide best‑in‑class service and reliability to connect a wide range of businesses, from entrepreneurs to enterprises, with their end users. The messaging platform is a mission‑critical system, responsible for delivering billions of messages, and must be architected for massive scale and reliability.

As a Senior Lead Software Engineer, you will have an overarching responsibility for the architecture, health, and scaling of the Messaging Infra platform with a focus on high‑volume message delivery. Your role will involve:

• Technical Strategy:
  Define the technical strategy and architectural vision for the Messaging Infra platform, ensuring all system improvements align with long‑term business goals for massive scalability, high reliability, and low latency message delivery.
• System Architecture and Improvement:
  Serve as the primary architect to build and improve high‑volume message delivery systems across multiple channels, focusing on throughput, performance, and reliability.
• Cohesive Technical Vision:
  Drive technical leadership to guide architectural decisions across multiple teams, striving towards a cohesive technical vision across multiple roadmap items and providing solutions for complex problems around scalability and performance.
• Platform Rollouts and Product Execution:
  Oversee and execute the planning and seamless rollout of major software releases and updates for the platform, managing the entire lifecycle from design to deployment in production environments including significant individual contributions.
• Problem Solving and Reliability:
  Act as a go‑to expert for diagnosing and resolving complex performance, scalability, and reliability issues across the messaging platform. Implement proactive monitoring and telemetry to identify and address problems before they become critical incidents.
• Mentorship:
  Mentor other engineers regularly, primarily experienced lead and senior engineers, to develop new technical leadership for the company.
• Cross‑functional
  
  Collaboration:
  
  Partner with product managers, deliverability and compliance specialists, and other stakeholders to gather requirements, resolve conflicts, and ensure alignment across all teams and projects.
• Continuous Improvement:
  Stay current with emerging technologies and industry trends, evaluating new tools and practices to identify how they can improve systems and internal processes.

• 12 years of experience in software development, strong knowledge of computer science fundamentals, domain‑driven design, and extensive expertise in architectural patterns, specifically within the domain of distributed systems.
• Have proven that you can build and scale complex distributed systems, including solving problems in sustainable ways, balancing pragmatic development with ideal architecture, breaking through technical obstacles with vigor, and leading teams through crises by working side by side with them in the trenches.
• BA or BS Degree in Computer Science, related field, or equivalent experience.
• Technical Expertise:
  Deep expertise in relevant programming languages (e.g., Python, Go) and cloud platforms (AWS, Azure, GCP), containerization (Kubernetes, Docker), and…