Guides
Short, practical answers to common e-mail, DNS, domain and password questions. Each guide links to the free tool that checks it.
- How to set up SPF, DKIM and DMARC: a step-by-step guide Set up SPF, DKIM and DMARC for your domain in the right order: list your senders, publish records, verify with free checkers and move DMARC to enforcement. 8 min read · updated
- Moving DMARC from p=none to p=reject without losing mail A practical plan for moving DMARC from p=none to quarantine and reject: read aggregate reports, fix failing senders, handle subdomains and forwarding. 7 min read · updated
- Gmail, Yahoo and Outlook bulk sender requirements: the 2026 checklist What Gmail, Yahoo and Outlook.com require from senders in 2026: SPF, DKIM, DMARC, alignment, one-click unsubscribe, spam-rate limits and how to check each item. 6 min read · updated
- Is my IP or domain blacklisted? How to check and get delisted How to check whether your mail server IP or domain is on a DNS blocklist, what a listing means, how to fix the cause and request removal. 6 min read · updated
- How long does DNS propagation take? TTLs and caching explained DNS propagation is really cache expiry. How TTLs, negative caching and name-server changes decide how fast a DNS change shows up, and how to speed it up. 5 min read · updated
- How to read e-mail headers and spot phishing Learn which e-mail headers to trust, how to read Received lines and Authentication-Results, and the warning signs of phishing — with a free header analyzer. 7 min read · updated
- How long should a password be? NIST SP 800-63B-4 explained What NIST SP 800-63B revision 4 says about password length, complexity rules, rotation and password managers — and what it means for your own passwords. 5 min read · updated
- WHOIS vs RDAP: how to find who owns a domain after the GDPR Why WHOIS shows "redacted", what RDAP changed after ICANN retired WHOIS for gTLDs in January 2025, and legitimate ways to reach a domain owner. 5 min read · updated
- SSL certificate not trusted? Fixing chain, hostname and expiry errors Fix "certificate not trusted" errors: missing intermediate certificates, hostname mismatches, expiry — and the 200/100/47-day certificate lifetime schedule. 6 min read · updated