[Hiring] Senior Systems Engineer - Email Deliverability & Infrastructure @Mission Inbox

Role Description

We are seeking a highly technical, impact-driven Senior Systems Engineer to own, scale, and protect our core email transmission infrastructure. In this role, your golden rule will be Reputation Above All. You are not just managing email lists or monitoring dashboards; you will architect and maintain the high-availability server infrastructure, Mail Transfer Agents (MTAs), and automated defensive systems that ensure our legitimate traffic hits the inbox while bad actors are ruthlessly contained.

The ideal candidate bridges the gap between deep Linux systems administration, network engineering, and advanced email deliverability strategy. You will have a massive impact on the company by safeguarding our global IP/domain reputation, minimizing blast radiuses, and ensuring zero-downtime mail operations across our entire infrastructure network.

Core Responsibilities

• Infrastructure Management & High Availability
  • MTA Optimization: Maintain and configure core MTAs (Postfix, Postal) and IMAP/POP3 servers (Dovecot), ensuring graceful reloads over restarts to prevent dropping active connections.
  • Traffic Routing & Load Balancing: Utilize HAProxy and network routing protocols (like BGP via FRRouting) to distribute outbound traffic and architect high-volume failover mechanisms.
  • Redundancy & Failover: Administer backend infrastructure databases (PostgreSQL replica setups) and maintain dedicated "Block" backup/archive servers to instantly take over the workload of a failed primary "Cube" server.
  • Architectural Segregation: Maintain strict workload isolation across our infrastructure network—separating standard nodes for mail stacks, specialized injection nodes (Postal), and separate archiving/backup systems to prevent high-volume senders from degrading performance.
• Deliverability Engine & Authentication Protocol Architecture
  • Protocol Enforcement: Act as the absolute technical authority on DNS and authentication setups, maintaining flawless configurations for SPF, DKIM, DMARC, and BIMI.
  • Traffic Throttling: Implement automated, MTA-level dynamic throttling to handle 4xx deferrals instantly, preventing a single high-volume sender from triggering global rate limits across our shared IP pools.
  • Warm-up Strategy: Design and guide automated IP/Domain Warm-up Plans for new infrastructure, managing incremental volume scaling over 2–4 week cycles.
• Edge Security, Anti-Abuse & Incident Response
  • Outbound Spam Filtering: Configure and optimize Rspamd to actively scan, flag, and quarantine highly spammy content before it exits our network.
  • Edge Defense: Deploy automated connection-dropping systems (Fail2Ban, custom SMTP blocker scripts) to mitigate authenticated attacks, brute-force attempts, and malicious traffic.
  • Blast Radius Mitigation: Program and maintain a dynamic IP pooling engine ("The Penalty Box") to instantly isolate accounts displaying poor metrics (bounces, FBL spikes) away from prime Tier-1 IP pools.
  • Blocklist Remediation: Act as the primary responder to major DNSBL listings. Leverage log analysis to locate the root cause account, plug the security leak, and submit expert delisting requests.
• Observability & Monitoring
  • Log Shipping Architecture: Build and manage high-performance log aggregation pipelines using Vector to ship system and MTA data into a centralized repository for real-time auditing and incident response.
  • Network Auditing: Utilize IPAudit and custom tools to continuously scan for bandwidth anomalies, connection spikes, or compromised user credentials.
  • Dashboard Management: Actively monitor ISP infrastructure portals daily along with third-party tracking tools.

Qualifications

• 5+ years of experience as a Linux Systems Administrator, DevOps, or Infrastructure Engineer with deep networking knowledge (TCP/IP, routing, ports, DNS management).
• Expert-level proficiency configuring, debugging, and optimizing enterprise mail tools such as Postfix, Dovecot, or Postal.
• Hands-on experience writing rules and maintaining mail-filtering/anti-abuse applications like Rspamd and Fail2Ban.
• Proven experience building or maintaining log pipelines using Vector or similar high-scale telemetry frameworks.
• Experience implementing network routing layer tools (HAProxy, FRRouting) and relational databases (PostgreSQL replication).
• Strong familiarity with automated SSL/TLS certificate rotation and multi-node compliance monitoring.

Requirements

• Deep comprehension of the difference between Delivery (server handoff) and Deliverability (inbox placement).
• Expert parsing of aggregate DMARC reports using platforms like DMARCian, Valimail, or Postmark.
• Strict commitment to Acceptable Use Policies (AUP): zero tolerance for purchased/scraped lists and a firm grasp on Feedback Loop (FBL) automated triage.

Key Performance Indicators (KPIs)

• Global Infrastructure Spam Complaint Rate: Maintained strictly under 0.1%.
• Global Hard Bounce Rate: Kept consistently below 2.0%.
• Infrastructure Uptime: 99.99% availability across all outbound MTAs and mail relays.
• Incident Isolation Time: Transitioning high-risk or abusive senders to the "Penalty Box" or circuit-breaking campaigns within minutes of a threshold breach.

This is a highly technical systems engineering role, not a marketing or email campaign management position. To be considered, you must have hands-on experience configuring Linux mail servers at the command-line level. Please confirm upon applying that the fixed compensation range of $50,000 to $72,000 USD per year aligns with your expectations.