Infrastructure & Data Engineer | Email deliverability, DNS, PostgreSQL, verification tooling

I run VSN j.d.o.o., a one-person software company in Osijek, Croatia. Nothing is subcontracted — you deal with the person doing the work. EU-based, invoicing in EUR with a Croatian VAT ID.

EMAIL AUTHENTICATION AND DNS. SPF and the ten-lookup limit that fails silently. DKIM selectors and keys that DNS panels quietly truncate. DMARC policy, alignment and aggregate report analysis. MX and mail routing. Blacklist checks (Spamhaus, SpamCop, Barracuda). Diagnosis from real headers and bounce logs. I built my own diagnostic for this after a commercial checker reported a DMARC record as missing that demonstrably existed — a recursive resolver had cached the negative answer. Mine queries the domain's authoritative nameservers and reports "could not determine" separately from "absent", because a tool that confuses those sends people to publish a duplicate record and break authentication that was working.

DATA PIPELINES AND VERIFICATION. Parsers that turn messy CSV, PDF and ledger exports into structured data, where anything unresolved is flagged rather than guessed. I build duplicate-payment detection software commercially. I validated my own scanner against 385,347 published payment records carrying invoice-level ground truth: four of its six detection rules had precision under 4%, and a placeholder-reference bug was producing roughly 2.9 million false findings from a single repeated string. I disabled the four rules and fixed the bug rather than ship numbers I could not defend. Output went from ~3,277,000 findings to 49, of which 29 are genuine duplicate-payment candidates.

CODE REVIEW. Reading code I did not write — increasingly code generated by AI tools — to find what is actually wrong rather than what looks wrong, and reporting it ranked by consequence.

INFRASTRUCTURE. Cloudflare Workers, KV and DNS. Vercel. PostgreSQL. Linux. Git.

TECHNOLOGIES: DNS, SPF, DKIM, DMARC, DNSSEC, email deliverability, email authentication, mail routing, MX, Postfix, DNSBL, Cloudflare, Cloudflare Workers, Cloudflare KV, Vercel, PostgreSQL, SQL, Python, TypeScript, JavaScript, Node.js, Next.js, React, REST API, ETL, data migration, CSV parsing, PDF parsing, data validation, code review, application security, Linux, Git.

INDUSTRIES: finance and accounts payable, public sector spending data, SaaS, small business IT.

Working language English. Written communication preferred — I answer the same day.