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
Three areas, and the combination is the unusual part. Most people in email have one of them.
Email infrastructure. Building and operating the transport layer. 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
| Role | Organisation | Period |
|---|---|---|
| Infrastructure Engineer | Pipedrive, Tallinn | 2022 to present |
| Technical Consultant, Email Infrastructure | Adobe, Bangalore | 2020 to 2022 |
| Email Infrastructure Lead | Experiture Omni-Channel Marketing Platform | 2019 to 2020 |
| Email Deliverability Specialist | Zeta Global, Hyderabad | 2018 to 2019 |
| Technology Executive, Email Deliverability | IntraSoft Technologies Limited (123Greetings.com), Kolkata | 2015 to 2018 |
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.
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.
Writing
He maintains an SMTP response reference: what the responses in a mail log actually mean, whether retrying helps, and what to change so they stop. It is written from operating these systems rather than from the specifications.