Dns

DNS configuration, troubleshooting, and command-line lookup tools.

Rspamd mail filtering and DKIM signing illustration

Jul 28, 2026 • 8 min read • series

Install and Integrate Rspamd on Ubuntu 26.04

Install Rspamd on Ubuntu 26.04, connect it to Postfix as a milter, configure Redis, and publish DKIM and DMARC records for your mail domain.

PostfixAdmin dashboard illustration with mailboxes and aliases

Jul 27, 2026 • 9 min read • series

Set up PostfixAdmin on Ubuntu 26.04

Set up PostfixAdmin on Ubuntu 26.04 with Nginx, PHP, MySQL, DNS records, and a Let's Encrypt certificate for a virtual mail server.

Email envelope passing SPF, DKIM, and DMARC authentication checks

Jul 17, 2026 • 8 min read

Email Authentication Explained: SPF, DKIM, and DMARC

SPF, DKIM, and DMARC help prevent domain spoofing. See how each check works, what DMARC alignment requires, and how to verify the DNS records with dig.

Jun 26, 2026 • 7 min read

How to Edit Your Hosts File on Linux, Windows, and macOS

The hosts file maps domain names to IP addresses locally, overriding DNS. This guide explains how to edit /etc/hosts on Linux, macOS, and Windows with examples for testing, blocking, and local development.

Jun 14, 2026 • 6 min read

host Command in Linux: DNS Lookup

The host command is a simple DNS lookup tool. This guide covers forward and reverse lookups, querying specific record types, using a chosen name server, and reading the output.

Running DNS lookups with the host command in a Linux terminal

May 25, 2026 • 8 min read

nslookup Command in Linux: Query DNS Records

The nslookup command queries DNS servers for domain records. This guide covers A, MX, NS, TXT, and AAAA lookups, reverse DNS, interactive mode, and choosing a specific name server.

nslookup command querying DNS records in a Linux terminal

May 25, 2026 • 12 min read

dig Command in Linux: DNS Lookup

The dig command is a DNS lookup tool for querying name servers. This guide covers querying record types, reverse lookups, tracing resolution paths, and verifying DNSSEC.

Dig command querying DNS records in a Linux terminal

May 25, 2026 • 7 min read

whois Command in Linux: Query Domain Registration Info

The whois command looks up domain registration, registrar, name server, expiry, IP allocation, and AS number details from Linux.

Querying domain registration with the whois command in Linux

Aug 21, 2019 • 4 min read

How to Set DNS Nameservers on Ubuntu 18.04

The DNS nameservers (resolvers) are servers which are used by other devices to perform DNS lookup for a requested domain. In this guide, we’ll explain how to configure the DNS nameservers (resolvers) on Ubuntu 18.04.

Set/Change DNS nameservers on Ubuntu 18.04