About
About Rastu Singh
Rastu Singh is an email infrastructure engineer based in Tallinn, Estonia. He specialises in the systems that carry high-volume email: MTA platforms, SMTP transport, sender reputation, and the authentication stack of SPF, DKIM and DMARC. He currently works as an Infrastructure Engineer at Pipedrive, and has worked on email infrastructure and deliverability since 2015.
What he does
Email infrastructure. Building and operating the transport layer at scale: estates running to over a thousand sending IPs and delivering millions of messages a day. Six MTAs in production across his career: PowerMTA, KumoMTA, Momentum, Postfix, Haraka and GreenArrow. Queue policy, per-domain and per-provider throttling, connection and concurrency limits, retry and backoff strategy, multi-datacenter routing, and the DNS underneath it. He has built sending estates from nothing on bare metal and cloud, and automated them with Ansible, Terraform, Python and Bash.
Deliverability. Inbox placement and sender reputation at volume, across both high-volume B2C marketing and transactional sending and B2B outbound infrastructure. IP and domain warm-up, shared and dedicated pool design, bounce and deferral classification, feedback loop processing, suppression and sunset policy, and direct escalation with mailbox providers when mail is being throttled or blocked. He has cleared a Spamhaus listing that had stopped enterprise delivery outright, restoring it inside 48 hours.
Email security. SPF, DKIM key rotation, DMARC policy progression toward enforcement, ARC, BIMI, MTA-STS and TLS-RPT. Anti-spam tuning with SpamAssassin and Rspamd, abuse prevention, open-relay protection, and reducing domain spoofing and phishing exposure without breaking legitimate mail flow.
Career
Infrastructure EngineerPipedrive · Tallinn, Estonia2022 – present17 achievements
- Cut environment provisioning and deploy time by ~70% and eliminated configuration drift between staging and production by codifying multi-datacenter email infrastructure in Terraform and Ansible.
- Removed ~15 hrs/week of manual delivery operations by building automated bounce processing, feedback-loop handling, and data-sync tooling.
- Own inbox placement and sender reputation across Gmail, Yahoo, Microsoft/M365, and regional ISPs, monitoring Postmaster Tools and SNDS signals to drive remediation before provider throttling escalates into hard blocking.
- Held user-reported complaint rates under Gmail's 0.3% threshold and reached bulk-sender compliance ahead of the enforcement deadline by implementing DMARC alignment and one-click List-Unsubscribe across sending domains.
- Sustained delivery stability at millions of messages per day across global mailbox providers by tuning high-throughput PowerMTA clusters: queue policies, per-provider throttling, connection and concurrency limits, and retries and backoff strategy.
- Closed domain-spoofing and TLS-downgrade exposure by owning the authentication stack end to end: SPF, DKIM key rotation, DMARC policy progression toward enforcement, MTA-STS, and TLS-RPT.
- Reduced time-to-diagnosis on delivery incidents by classifying bounces, deferrals, and feedback-loop events into per-provider, per-domain, and per-IP diagnostics from raw MTA logs.
- Cut mean time to detection for delivery degradation by instrumenting queue depth, deferral rate, per-provider latency, and reputation signals as first-class SLOs with proactive alerting in Prometheus, Grafana, and Zabbix.
- Produce deliverability reporting and strategic recommendations for leadership, translating delivery rate, bounce, complaint, and engagement metrics into prioritized remediation plans and roadmap input.
- Protect established sender reputation by designing IP pool strategy and warm-up execution across hundreds of shared and dedicated pools, using reputation-aware routing to isolate risky traffic.
- Delivered the BIMI/VMC rollout as a brand-trust and anti-phishing control, and hardened transport with enforced TLS and DNSSEC.
- Operate and scale outbound email infrastructure across multiple data centers and an estate of 1,000+ sending IPs delivering millions of messages per day, owning capacity, queueing, redundancy, and failover as the system of record for platform delivery.
- Shortened build time on internal delivery tooling by using LLM-assisted development (Claude Code) to scaffold, refactor, and review automation for bounce processing, reporting, and provisioning, with human verification and staged rollout before any change reaches production sending.
- Cut time-to-root-cause on delivery incidents by using LLM-assisted analysis of MTA logs and mailbox-provider response patterns to surface candidate causes across per-domain and per-IP data faster than manual log review.
- Operate the Linux hosts behind the sending platform: systemd service and timer orchestration, journald and MTA log analysis, firewall and network configuration, and performance troubleshooting under production load.
- Lead incident response for delivery-affecting events, driving root-cause analysis, runbooks and documentation, and the follow-up automation that stops the same class of failure recurring.
- Partner with security, product, and DevOps to build abuse-resistant sending controls into the platform.
Technical Consultant (Email Infrastructure)Adobe · Bangalore, India2020 – 202210 achievements
- Restored full delivery within 48 hours after a Spamhaus listing crippled enterprise client mail, by root-causing the emitting source and coordinating remediation directly with Spamhaus.
- Cut client onboarding time by ~50% and improved cross-environment consistency by automating multi-region provisioning and configuration management with Terraform and Ansible.
- Owned deliverability strategy for enterprise marketing and transactional senders, covering inbox placement, reputation, list hygiene, engagement segmentation, and sunset policy across large B2C programs.
- Architected and operated PowerMTA, Momentum, and Postfix platforms for enterprise marketing and transactional workloads at high throughput.
- Migrated and consolidated client sending platforms with zero-downtime cutovers, preserving established IP and domain reputation through each transition.
- Reduced client domain-spoofing exposure by implementing SPF, DKIM, and DMARC across client domains and driving policy progression from monitoring to enforcement.
- Kept sender reputation healthy across client onboardings by designing IP allocation and warm-up frameworks with feedback-loop integrations.
- Resolved blocking and throttling at Gmail, Microsoft, Yahoo, and regional providers through direct ISP escalation and postmaster relationships.
- Advised enterprise clients on CAN-SPAM and GDPR compliance, consent handling, and anti-abuse controls.
- Ran technical workshops, architecture reviews and written SOPs that transferred deep infrastructure and deliverability knowledge to client engineering and marketing teams, leaving them able to operate the platform themselves.
Email Infrastructure LeadExperiture Omni-Channel Marketing Platform · Contract2019 – 20206 achievements
- Built the platform's SMTP sending infrastructure from scratch: MTA selection and deployment, server and network build-out, IP allocation, queue and throttling policy, and the routing behind an omni-channel marketing product.
- Established the authentication layer from zero across all sending domains: SPF, DKIM, DMARC, MX and PTR/rDNS, with TLS on transport and Cloudflare in front of DNS.
- Planned and executed IP and domain warm-up for a brand new sending estate, taking it from no sending history to sustained production volume without tripping provider throttles.
- Set up bounce and complaint processing, suppression handling and delivery monitoring so the platform could be operated and debugged day to day.
- Led the IT team and a group of junior deliverability consultants, setting technical direction, reviewing their work and bringing them up to speed on authentication, warm-up and reputation practice.
- Owned the email infrastructure workstream end to end, from architecture decisions through to documentation and handover.
Email Deliverability SpecialistZeta Global · Hyderabad, India2018 – 20197 achievements
- Reduced block rates by ~30% during new-client ramp-up by designing staged IP warm-up frameworks instrumented with feedback-loop data.
- Tuned inbound spam filtering with SpamAssassin and Rspamd, managing rule sets, scoring thresholds and Bayes training to cut false positives without letting abuse through.
- Cut ~12 hrs/week of manual effort by automating provisioning, DNS configuration, and delivery reporting in Ansible and Bash.
- Owned deliverability for high-volume B2C sending across a multi-tenant client base as the primary escalation point for inbox placement and blocking incidents.
- Provisioned and tuned PowerMTA, Momentum, GreenArrow, and Postfix across regions for throughput, queue behavior, and reputation.
- Pre-empted blacklisting and authentication failures by monitoring reputation metrics and ISP feedback loops.
- Configured SPF, DKIM, DMARC, and rDNS/FCrDNS for new sending infrastructure as part of standard client onboarding.
Technology Executive (Email Deliverability)IntraSoft Technologies Limited (123Greetings.com) · Kolkata, India2015 – 20183 achievements
- Sustained delivery at 300,000 to 400,000 messages/day across US, UK, AU, CA, and ROW regions by owning campaign deployment and queue management.
- Improved inbox placement and reduced spam and phishing risk by configuring PowerMTA and implementing rDNS/FCrDNS, SPF, DKIM, and DMARC.
- Improved inbox placement by building and maintaining ISP and domain whitelisting relationships.
At Experiture he built the platform's SMTP sending infrastructure from scratch, established the authentication layer across all sending domains, and led the IT team and a group of junior deliverability consultants. At IntraSoft he ran campaign deployment and queue management at 300,000 to 400,000 messages per day across US, UK, AU, CA and ROW regions.
Stack
Open-source work
smtpsift classifies SMTP rejections and deferrals into a category and an action, on the argument that hard and soft bounce is too coarse to act on. dmarcsight audits a domain's email authentication posture, including the SPF ten-lookup limit and MTA-STS policy and MX consistency, which generic checkers miss.