Resource Articles
Practical guides and explainers for DNS, email security, certificates, and troubleshooting.
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DNS Basics Articles
Read DNS basics articles covering records, nameservers, DNSSEC, propagation, and core lookup concepts.
Email Security Articles
Read practical guides on SPF, DMARC, DKIM, BIMI, MTA-STS, and related email authentication topics.
DNS Troubleshooting Articles
Read troubleshooting guides for propagation, mail issues, DNS misconfiguration, and common operational failures.
Setup And Migration Guides
Read setup and migration guides for common DNS and email configuration tasks.
Networking Articles
Read networking articles covering subnetting, CIDR notation, IP ranges, and related infrastructure basics.
Certificate Security Articles
Read certificate-focused articles covering CAA records and related certificate issuance controls.
Featured Email Authentication Guides
How to Check a DKIM Record
A practical guide to checking a DKIM record, finding the right selector, validating the TXT record, and spotting common DKIM setup problems.
How to Check a DMARC Record
A practical guide to checking a DMARC record, understanding the main tags, and spotting common DMARC issues before enforcement causes problems.
How to Check an SPF Record
A practical guide to checking an SPF record, including where to look, how to read includes and qualifiers, and how to spot common SPF problems.
How to Check Email Security for a Domain
A practical workflow for checking email security for a domain, including SPF, DMARC, DKIM, MX, MTA-STS, TLS-RPT, BIMI, and provider setup.
SPF vs DKIM vs DMARC: What Is the Difference?
Learn the difference between SPF, DKIM, and DMARC, how they work together, and why you usually need all three for a strong email authentication setup.
Featured Provider Setup Guides
Google Workspace SPF, DKIM, and DMARC Setup
A practical guide to setting up SPF, DKIM, and DMARC for Google Workspace, including what to publish in DNS and what to verify after setup.
How to Check Google Workspace DNS
A practical guide to checking Google Workspace DNS records, including MX, SPF, DKIM, DMARC, and the signs of a mixed or incomplete setup.
How to Check Microsoft 365 DNS
A practical guide to checking Microsoft 365 DNS records, including MX, autodiscover, SPF, DKIM, DMARC, and the signs of an incomplete migration.
Microsoft 365 SPF, DKIM, and DMARC Setup
A practical guide to setting up SPF, DKIM, and DMARC for Microsoft 365, including the DNS records to publish and the checks to run after setup.
Networking
What Is APIPA? 169.254.x.x Explained
Learn what APIPA means, why devices assign 169.254.x.x addresses, what it says about DHCP problems, and how to troubleshoot a link-local IP quickly.
Private vs Public IP Addresses Explained
Learn the difference between private and public IP addresses, how special-use ranges fit in, and why correct IP classification matters in troubleshooting.
CIDR Cheat Sheet for Common Subnet Sizes
Use this CIDR cheat sheet to quickly compare common subnet sizes, masks, block sizes, and usable host counts during subnet planning and troubleshooting.
How to Calculate a Subnet Range Step by Step
A practical guide to calculating network address, broadcast address, and usable host range from an IP address and subnet size.
What Is a Subnet Mask? Explained Clearly
Learn what a subnet mask does, how it separates network and host portions of an IPv4 address, and how it relates to CIDR and usable ranges.
What Is CIDR Notation? Explained with Examples
Learn what CIDR notation means, how slash prefixes like /24 and /27 define IP ranges, and how CIDR relates to subnet masks and routing.
DNS Basics
What Is DNS TTL? Time to Live Explained
Learn what DNS TTL means, how DNS caching works, why TTL affects propagation and reliability, and how to choose the right TTL before a DNS change.
What Is an SRV Record in DNS?
Learn what an SRV record is, how service, protocol, priority, weight, and port fields work, and when SRV lookups are useful in real deployments.
How to Read MX Records and Mail Priorities
A comprehensive guide to MX records. Learn how MX records work, how priority is calculated, how mail routing functions, and how to troubleshoot delivery issues.
What are glue records?
Learn what glue records are, when they are required, and why they are critical for keeping in-bailiwick nameserver delegation resolvable.
What Are TXT Records in DNS?
Learn what DNS TXT records are, how they are used for verification and email authentication, and what to check when TXT records fail.
What is a CNAME record?
A practical reference guide to CNAME records, including what the alias target means, common examples, and where CNAMEs can cause confusion.
What is a DNS record?
A practical reference guide to DNS records, including what they contain, what common fields mean, and how different record types are used in real DNS setups.
What is a PTR record?
Learn what PTR records are, how reverse DNS works, and why accurate PTR validation matters for mail delivery, logging, and network trust.
What is a TXT record?
Learn what a DNS TXT record is used for, what TXT records look like, and why they are so common in verification and email security setups.
What Is an A Record? DNS A Record Explained
Learn what an A record is, how it maps a hostname to an IPv4 address, where it is used, and how to troubleshoot common A record issues.
What Is an AAAA Record? DNS AAAA Record Explained
Learn what an AAAA record is, how it maps a hostname to an IPv6 address, when to use it, and how to troubleshoot common AAAA record issues.
What is an NS record?
Learn what NS records do, how nameserver delegation works, and how to troubleshoot DNS authority and resolution issues in real-world setups.
What is DNS propagation?
Learn what DNS propagation means, why different resolvers may show different answers, and what to check during a DNS change.
What Is DNS? Domain Name System Explained
Learn what DNS is, how DNS resolution works, what common record types do, and why DNS is essential for websites, email, and online services.
What Is DNSSEC? DNS Security Extensions Explained
Learn what DNSSEC is, how DNSKEY and DS records work together, and why DNSSEC matters for protecting DNS integrity and trust.
Certificate Security
How to Check Certificate SANs and Spot Hostname Mismatches
Learn how to check certificate SANs, confirm whether a hostname is covered, and use SAN data to troubleshoot TLS errors and asset exposure.
How to Fix CAA Record Errors Before Certificate Renewal Fails
Learn how to fix CAA record errors, why certificate issuance gets blocked, and how to verify issue, issuewild, and parent-domain policy before renewal fails.
How Certificate Transparency Helps Find Subdomains
Learn how certificate transparency logs help find subdomains, what the data misses, and how to interpret CT-based hostname discovery safely.
What Is a Subject Alternative Name in TLS?
Learn what a subject alternative name is in a TLS certificate, why SANs matter for hostname validation, and how SAN data helps with discovery and troubleshooting.
What are CAA records?
Learn what CAA records contain, how issue and issuewild tags work, and how CAA helps control which certificate authorities can issue for your domain.
Troubleshooting
How to Fix SPF Softfail
A practical guide to fixing SPF softfail, including how to identify the sending domain, review the SPF policy, authorise senders, and tighten enforcement safely.
How to Check an MX Record
A practical guide to checking an MX record, reading priorities and targets, and confirming whether mail is routed to the provider you expect.
How to Fix DKIM Failures
A practical guide to fixing DKIM failures, including wrong selectors, missing records, bad key publication, and signing problems in email platforms.
How to Fix DMARC Failures
A practical guide to fixing DMARC failures, including SPF and DKIM alignment issues, missing records, third-party senders, and enforcement problems.
How to Fix MX Record Problems
A practical guide to fixing MX record problems, including wrong targets, bad priorities, mixed providers, and incomplete mail migrations.
How to Fix SPF PermError
A practical guide to fixing SPF PermError, including multiple SPF records, too many DNS lookups, syntax mistakes, and broken includes or redirects.
What Is a Dangling CNAME?
Learn what a dangling CNAME is, why it can create subdomain takeover risk, what patterns to look for, and how to clean up stale aliases safely.
Common Glue Record Problems: DNS Delegation Issues Explained
A troubleshooting guide to glue record issues, including in-bailiwick nameservers, missing glue, delegation mismatches, and how to fix DNS resolution failures.
Common PTR Record Problems: Reverse DNS Issues Explained
A practical guide to PTR record problems, including missing reverse DNS, forward-confirmed reverse DNS, hostname issues, and how PTR impacts email deliverability.
How to Check DKIM Selectors (Step-by-Step Guide)
Learn how to find and check DKIM selectors, query DNS correctly, and troubleshoot missing or invalid DKIM records with real examples.
How to Check DNS Propagation
A practical guide to checking DNS propagation, including what to compare, how TTL affects results, and how to interpret inconsistent answers.
How to Check DNSSEC (Step-by-Step Guide)
A practical DNSSEC checking guide covering DNSKEY and DS records, signature validation, and how to verify the full DNSSEC chain of trust.
How to Check MTA-STS
Learn how to validate MTA-STS using both the DNS TXT record and the hosted HTTPS policy file, including common issues and troubleshooting steps.
How to Check Reverse DNS for Mail (Step-by-Step Guide)
A practical guide to checking reverse DNS for mail servers, including PTR records, forward confirmation (FCrDNS), and what good mail-related reverse DNS looks like.
How to Check Whether an SPF Record Is Too Complex
A practical SPF troubleshooting guide covering recursive includes, DNS lookup limits, redirect behaviour, and how to simplify an overly complex SPF policy.
How to Interpret DMARC Reports
A practical guide to interpreting DMARC reports, identifying legitimate senders, spotting spoofing, and deciding when to move toward enforcement.
How to Publish BIMI (Step-by-Step Guide)
A practical guide to publishing BIMI, including record format, selector usage, logo requirements, and what to validate before rollout.
How to Read Email Headers (With Examples)
Learn how to read email headers with real examples, including Authentication-Results, Received headers, Return-Path, and how to trace message flow.
How to Troubleshoot DMARC Failures
A practical DMARC troubleshooting guide covering missing records, alignment problems, policy interpretation, and common causes of DMARC failure.
How to Troubleshoot MX Record Problems
A practical MX troubleshooting guide covering missing MX records, wrong targets, bad priorities, and how to verify mail routing during migrations.
How to Troubleshoot SPF Failures: Complete Step-by-Step Guide
A comprehensive SPF troubleshooting guide covering missing records, multiple SPF issues, DNS lookup limits, includes, redirects, and how to fix SPF failures.
When to use SPF flattening
Learn when SPF flattening may help, when it creates more operational risk than value, and what to review before using it in production.
Why does a domain have multiple MX records?
Learn why multiple MX records are normal, how priority works, and what to check when a domain publishes more than one receiving mail host.
Why does one hostname resolve to multiple IP addresses?
Learn why a single hostname may return multiple A or AAAA answers and how to interpret that in DNS and email troubleshooting.
Guides
Google Workspace SPF, DKIM, and DMARC Setup
A practical guide to setting up SPF, DKIM, and DMARC for Google Workspace, including what to publish in DNS and what to verify after setup.
How to Check Email Provider Setup for a Domain
A practical workflow for checking whether a domain's email provider setup looks like Google Workspace, Microsoft 365, or a mixed environment with extra gateways.
How to Check Email Security for a Domain
A practical workflow for checking email security for a domain, including SPF, DMARC, DKIM, MX, MTA-STS, TLS-RPT, BIMI, and provider setup.
How to Check Google Workspace DNS
A practical guide to checking Google Workspace DNS records, including MX, SPF, DKIM, DMARC, and the signs of a mixed or incomplete setup.
How to Check Microsoft 365 DNS
A practical guide to checking Microsoft 365 DNS records, including MX, autodiscover, SPF, DKIM, DMARC, and the signs of an incomplete migration.
Microsoft 365 SPF, DKIM, and DMARC Setup
A practical guide to setting up SPF, DKIM, and DMARC for Microsoft 365, including the DNS records to publish and the checks to run after setup.
How to Check DNS Delegation Correctly
Learn how to check DNS delegation by comparing parent and child NS records, SOA responses, and glue records to find broken or inconsistent delegation.
How to Check If an IP or Domain Is Blacklisted
Learn how to check whether an IP address or domain is blacklisted, what DNSBL results really mean, and how to interpret blocklist findings before escalating.
How to Identify a Hosted Service from DNS Clues
Learn how to identify a hosted service or platform from DNS clues such as CNAME targets, MX patterns, TXT records, and provider-specific hostname conventions.
How to Read CAA Records Correctly
Learn how to read CAA records, understand issue, issuewild, and iodef tags, and tell whether certificate issuance is properly restricted for a domain.
How to Read CNAME Chains Correctly
Learn how to read CNAME chains, understand alias targets step by step, and spot stale, looping, or takeover-prone CNAME configurations.
How to Read DKIM Records Correctly
Learn how to read DKIM records, understand selector hostnames and key tags, and spot the difference between valid publishing and weak configurations.
How to Read DNS Audit Results
Learn how to read DNS audit results, separate important findings from noise, and turn a broad DNS report into a practical remediation plan.
How to Read NS Records Correctly
Learn how to read NS records, understand what they say about delegation, and spot signs of stale nameservers, mismatches, or broken authority.
How to Read SPF Records Correctly
Learn how to read an SPF record, understand mechanisms and qualifiers, spot risky syntax, and tell whether an SPF policy is too broad or too complex.
How to Read TXT Records Correctly
Learn how to read TXT records, tell verification values from policy records, and spot common TXT mistakes in email and service setups.
How to Read WHOIS and RDAP Results
Learn how to read WHOIS and RDAP results, including registrar data, domain statuses, nameservers, key dates, and common reasons records look incomplete.
How to Run a DNS Audit That Finds Real Issues
Learn how to run a DNS audit that checks core DNS, delegation, email security, stale records, and provider patterns without missing the issues that matter most.
How to Tell Which Email Provider a Domain Uses
Learn how to tell whether a domain uses Google Workspace, Microsoft 365, or another mail provider by reading MX, SPF, DKIM, and related DNS patterns.
How to Use a DNS Summary Effectively
Learn how to use a DNS summary view to spot missing records, provider patterns, email risks, and inconsistent DNS data before digging deeper.
DNS Records Required for Google Workspace (Complete Setup Guide)
Complete guide to Google Workspace DNS records including MX, SPF, DKIM, DMARC, and domain verification. Includes real record examples and setup best practices.
DNS Records Required for Microsoft 365 (Complete Setup Guide)
Complete guide to Microsoft 365 DNS records including MX, SPF, CNAME, DKIM, and DMARC. Includes real record examples and migration best practices.
Email Security
How to Check a DKIM Record
A practical guide to checking a DKIM record, finding the right selector, validating the TXT record, and spotting common DKIM setup problems.
How to Check a DMARC Record
A practical guide to checking a DMARC record, understanding the main tags, and spotting common DMARC issues before enforcement causes problems.
How to Check an SPF Record
A practical guide to checking an SPF record, including where to look, how to read includes and qualifiers, and how to spot common SPF problems.
Return-Path vs From Address: What's the Difference?
Learn the difference between the Return-Path and From address in email, why SPF checks one while DMARC protects the other, and how mismatches affect deliverability.
SPF vs DKIM vs DMARC: What Is the Difference?
Learn the difference between SPF, DKIM, and DMARC, how they work together, and why you usually need all three for a strong email authentication setup.
What Is a DMARC Record? Tags, Policy, and Examples
Learn what a DMARC record is, what the main DMARC tags mean, how policy works, and how to review a DMARC record correctly.
What Is an SPF Record? Syntax, Mechanisms, and Limits
Learn what an SPF record is, how SPF syntax and mechanisms work, what qualifiers mean, and what to check when reviewing an SPF policy.
What Is BIMI? Email Brand Indicators Explained
A practical guide to BIMI, including what the BIMI record contains, how selector-based publishing works, and how BIMI fits into email trust.
What Is DKIM and How Does It Work?
Learn what DKIM is, how DKIM works, what a selector does, what the public key record contains, and why DKIM matters for email authentication.
What Is DMARC and How Does It Work?
Learn what DMARC is, how DMARC uses SPF and DKIM alignment, what policy modes mean, and how DMARC helps prevent domain spoofing.
What Is MTA-STS? SMTP TLS Policy Explained
Learn what MTA-STS is, how it enforces TLS for email delivery, what the policy looks like, and how it works with DNS and HTTPS.
What is SPF and how does it work?
Learn what SPF is, how SPF records are evaluated, what include and all mechanisms mean, and how to troubleshoot common SPF problems.
What is SPF flattening?
A practical guide to SPF flattening, including what a flattened record looks like, why teams consider it, and what risks it introduces.
What Is TLS-RPT? SMTP TLS Reporting Explained
A practical reference guide to TLS-RPT, including what the record looks like, what the tags mean, and how it fits alongside MTA-STS.