214 answers · updated weekly
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Short, direct answers across DNS, email authentication, SSL/TLS, and domain security. Each on its own page — no scrolling a long article to find the one line you need.
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DEVELOPER · LEARNING
What Is a JWT? Are UUIDs guaranteed to be unique? Can I revoke a JWT before it expires? Can I use UUID as a primary key? How do I verify a JWT signature without the secret? How much larger does Base64 make my payload? Is a JWT encrypted or just signed? Is Base64 encryption or just encoding? Is a JWT encrypted or just signed? Is MD5 secure for password hashing? Should I store a JWT in localStorage or a cookie? Should I store a JWT in localStorage or a cookie? What hash function should I use for passwords? What is the 'alg: none' JWT vulnerability? What is the difference between bcrypt and Argon2? What is the difference between Base64 and Base64URL? What is the difference between HS256 and RS256? What is the difference between JWT and session cookies? What is the difference between MD5 and SHA-1? What is the difference between MD5 and SHA-256? What is the difference between UUID v4 and UUID v7?
DNS RECORDS · LEARNING
DNS Record Types Explained: A, AAAA, CNAME, MX, TXT, and More Can I have multiple A records for the same domain? Can I use Cloudflare DNS with any registrar? How do I add a TXT record in GoDaddy? How do I add a TXT record in Namecheap? How do I add a TXT record in Cloudflare? How do I add a TXT record in Route 53? How do I change nameservers in Namecheap? How do I change nameservers in GoDaddy? Should I use port 465 or port 587 for SMTP? What is DNS TTL and how does it affect changes? What is the difference between A and CNAME records? What is the difference between an A record and a CNAME? What is the difference between NS and SOA records? Why can't I use a CNAME at my root domain? Why does Cloudflare show my A record as flattened? Why is SMTP port 25 blocked by my ISP?
EMAIL AUTH · LEARNING
What Is DMARC? How It Stops Email Spoofing Do I need DMARC if I already have SPF and DKIM? Does Cloudflare proxy break DMARC? How do I set up DMARC for Google Workspace? How do I set up DMARC for Microsoft 365? How do I verify my Mailchimp DMARC alignment? How do I verify my SendGrid DMARC alignment? What is a DMARC aggregate report (rua)? What is DMARC alignment? What is the difference between DMARC p=none, p=quarantine, and p=reject? What should a DMARC RUA address look like? Why does my Google Workspace email fail DMARC? Will DMARC break my email if I set p=reject too quickly?
EMAIL AUTH · LEARNING
What Is an SPF Record? Sender Policy Framework Explained Can I have two SPF records? Does SPF protect the From: address users see? How do I combine SPF for multiple email providers? How do I set up SPF for Google Workspace? How do I set up SPF for Microsoft 365? How do I set up SPF for Zoho Mail? What happens if my domain has no SPF record? What is the difference between ~all and -all? What is the SPF 10-lookup limit? What SPF include should I use for HubSpot?
EMAIL AUTH · LEARNING
What Is DKIM? How DomainKeys Identified Mail Works Can I have multiple DKIM keys for the same domain? Does DKIM prevent spam? How do I add a CNAME for Office 365 Autodiscover? How do I find the DKIM selector for Google Workspace? How do I find the DKIM selector for Microsoft 365? How do I know if my DKIM key is rotating? What happens if my DKIM key is compromised? What is a DKIM selector? Why do some legitimate emails fail DKIM?
NETWORKING · LEARNING
What Is a MAC Address? Hardware Identifier, OUI, and Privacy Explained Can a MAC address identify me on the internet? Can I change my MAC address? How do I find a device's manufacturer from its MAC address? How do I find my public IP address? How do I read a traceroute? What is a locally administered MAC address? What is the difference between a MAC address and an IP address?
DNS RECORDS · LEARNING
What Is a CAA Record? Certificate Authority Authorization Explained DOMAINS · LEARNING
DomainScan API + MCP: The Developer Guide SECURITY · LEARNING
What Is Typosquatting? (And How Zscaler Found 30,000 Lookalikes) GETTING STARTED · HELP
DomainScan API Quickstart SECURITY · LEARNING
HTTP Security Headers Explained: HSTS, CSP, X-Frame-Options, and the Rest SECURITY · LEARNING
What Is a Subdomain Takeover? (And Why Microsoft Had 670 of Them) SECURITY · LEARNING
Enterprise Downtime Costs $300K/hr — And Why That's a Floor How do I calculate my own hourly downtime cost? How does Gartner's $5,600/minute figure compare to ITIC's data? What are the main causes of unplanned enterprise downtime? What counts as downtime cost in these reports? What is the current benchmark cost of one hour of downtime? Why is the $300K/hour figure called a floor and not a ceiling?
NETWORKING · LEARNING
CIDR Subnet Math Explained: /24, /16, /8, and Everything Between SECURITY · LEARNING
What Is a Domain or IP Blacklist? How Blocklists Work SECURITY · LEARNING
What Is a Phishing Link? How to Spot and Avoid Them DOMAINS · LEARNING
What Is Domain Age? Why It Matters for SEO, Trust, and Scam Detection DNS RECORDS · LEARNING
How DNS Propagation Actually Works (And Why 24 Hours Is a Lie) DNS RECORDS · LEARNING
What Is an SOA Record? The DNS Zone's Control File Explained EMAIL AUTH · LEARNING
What Is Domain Reputation and Why Does It Affect Email? SECURITY · LEARNING
What Is DANE? TLSA Records and DNS-Anchored TLS Explained SECURITY · LEARNING
What Is an SSL Certificate? TLS, HTTPS, and Trust Explained EMAIL AUTH · LEARNING
How to Read a DMARC Report (Aggregate XML Explained) DNS RECORDS · HELP
How to Read DNS Records: A Practical Guide SECURITY · HELP
What Does My Domain Trust Score Mean? SECURITY · HELP
How to Check If a Domain Is Blacklisted (Step-by-Step) DNS RECORDS · HELP
How to Monitor Your Domain's Health (DNS, SSL, Blacklists) EMAIL AUTH · HELP
How to Add a DMARC Record (Step-by-Step for Any Domain) GETTING STARTED · HELP
DomainScan MCP Quickstart (Model Context Protocol) EMAIL AUTH · HELP
How to Fix SPF Failures (softfail, hardfail, permerror) SECURITY · HELP
How to Tell If a Website Is Legitimate (7 Checks) DNS RECORDS · HELP
Understanding DNS Propagation EMAIL AUTH · HELP
Troubleshooting Email Deliverability Problems SECURITY · HELP
How to Check If Your Domain or IP Is Blacklisted EMAIL AUTH · HELP
How to Check Email Authentication (SPF, DKIM, DMARC) GETTING STARTED · HELP
How to Read a DomainScan DNS Report