Articles & Guides
Useful resources for web developers and system administrators
Networking
How Roskomnadzor Blocks Websites: EAIS, TSPU, DPI
How Roskomnadzor blocks websites: the EAIS register, TSPU under Law 90-FZ, DPI filtering, and the difference between IP, DNS and DPI blocking.
HTTP
401 Unauthorized Error: What It Means and How to Fix It
401 Unauthorized means missing, expired or wrong credentials. Read the WWW-Authenticate challenge and fix it in curl, Postman, nginx and Apache.
HTTP
400 Bad Request: How to Fix It in Chrome, nginx and APIs
400 Bad Request means the server refused a malformed request. Fix it in Chrome, Edge, Firefox or Safari, raise nginx header limits, debug Postman and APIs.
Monitoring
Russia's internet blocklist in numbers: 131,000 domains (2026)
Enterno.io study: Russia's RKN registry holds 131,361 domains, 70% are international (not .ru), and 19% of the world's top sites are blocked. Data + method.
Monitoring
Security Headers Across Russia's Top Sites: a 50-Site Study
Enterno.io scanned 50 of Russia's top sites: only 2% use CSP, 25% use HSTS, and 57% score an F on security headers — while SSL/TLS hygiene is excellent.
Monitoring
Mail Server Monitoring: MX/SMTP/Blacklist
Mail server monitoring: checking MX, SMTP ports 25/465/587, TLS via openssl, blacklist status and alerts. Set up continuous mail monitoring in enterno.io.
Infrastructure
Warming Up a Sending Domain
Warm up a sending domain and IP for email: a day-by-day volume schedule, gradual ramp, starting with your most engaged subscribers, and reputation monitoring.
Infrastructure
Transactional Email Deliverability
How to make transactional email land: a dedicated subdomain, SPF/DKIM/DMARC, stream separation, and MX/SMTP monitoring — practical, battle-tested rules.
Infrastructure
Why Emails Bounce: Codes and Causes
Why emails bounce: SMTP 5xx and 4xx codes explained, the real causes — bad address, reputation block, SPF/DKIM/DMARC failure — and how to fix each one.
Infrastructure
Email Bounce Handling: Hard vs Soft
How to handle email bounces: the hard vs soft difference, SMTP 4xx and 5xx codes, suppression-list rules and automation to protect your sender reputation.