Guides
Written for the admin who has to fix it today. Each guide starts with the answer, shows real record syntax, lists the mistakes that cause most failures, and links the check that verifies your fix.
Deliverability & reputation
Why mail lands in spam or bounces, and how mailbox providers judge a sender.
- Gmail, Yahoo and Microsoft sender requirements, explainedupdated 26 October 2026
- How to get off an email blocklist (DNSBL)updated 26 October 2026
- How to read email headers: Received, Authentication-Results and DKIMupdated 26 October 2026
- Reverse DNS (PTR) for mail servers: setup and FCrDNSupdated 26 October 2026
- Why is my email going to spam? A diagnostic checklist for adminsupdated 26 October 2026
Email authentication
SPF, DKIM, DMARC and BIMI: how they work, how they fail, how to roll them out.
- BIMI: requirements and setup for a logo in the inboxupdated 26 October 2026
- DKIM selectors: finding, verifying and rotating keysupdated 26 October 2026
- DMARC alignment, explained: why SPF passes but DMARC failsupdated 26 October 2026
- DMARC from p=none to p=reject without breaking mailupdated 26 October 2026
- Fixing "SPF too many DNS lookups" (PermError)updated 26 October 2026
- SPF explained: how to read, write and audit an SPF recordupdated 26 October 2026
DNS operations
Records, nameservers, TTLs and changes that take effect when you expect.
- Changing nameservers (DNS providers) without downtimeupdated 26 October 2026
- DNS propagation and TTLs: why your change hasn't shown up yetupdated 26 October 2026
- MX records: how inbound mail finds your serverupdated 26 October 2026
IP & network
Who owns an address, how to report abuse, and what reachability tests really tell you.
- Ping, ICMP and what "unreachable" really meansupdated 26 October 2026
- Reading IP Whois and RDAP results: owner, network and abuse contactupdated 26 October 2026