Email authentication guides
Practical, no-nonsense guides to SPF, DKIM and DMARC. Fix what is broken and keep your mail out of spam.
What Is an MX Record and How Email Routing Works
A practical guide to MX records: what they contain, how priority values pick a receiving mail server, how MX differs from A and PTR records, and the common mistakes (CNAME targets, missing trailing dots) that break inbound email.
What Is a PTR Record (Reverse DNS) for Email?
A PTR record is the reverse DNS entry that maps a sending IP back to a hostname, and mailbox providers now require a valid forward-confirmed match to accept mail. This guide explains FCrDNS, where PTR lives, and how to check and fix it.
What Is the List-Unsubscribe Header (One-Click Unsubscribe)?
A practical guide to the List-Unsubscribe and List-Unsubscribe-Post headers, RFC 8058 one-click unsubscribe, the 48-hour processing rule, and how to implement both headers correctly.
What Is ARC (Authenticated Received Chain)?
ARC preserves the original SPF, DKIM, and DMARC results when a message passes through a forwarder or mailing list. This guide explains the three ARC headers, how receivers validate the chain, and how ARC relates to DMARC.
2026 Bulk Email Sender Requirements: Google, Yahoo, Microsoft
The current 2026 checklist covering Gmail, Yahoo, Microsoft, and Apple bulk sender rules: SPF, DKIM, DMARC alignment, one-click unsubscribe, spam rate limits, and the enforcement timeline that now returns permanent rejections.
Should You Send Email From a Subdomain?
A practical guide to sending marketing and transactional email from dedicated subdomains: why reputation isolation protects your root domain, how it interacts with DMARC alignment and the sp= tag, and how to set it up.
How to Find Where Your DNS Is Hosted (So You Can Add SPF, DKIM, and DMARC)
Before you can add SPF, DKIM, or DMARC, you have to find the provider that actually controls your DNS records. Your nameservers tell you exactly who that is, and it is often not the company you bought the domain from. This guide shows you how to look up your nameservers, tell your registrar apart from your DNS host, and jump straight to the right setup steps for Cloudflare, GoDaddy, Namecheap, or Route 53.
What DNS Records Does Your Domain Need to Send and Receive Email?
A complete, ordered map of the DNS records a domain needs to send and receive email: MX and its A/AAAA target to receive, SPF, DKIM and DMARC to authenticate, plus optional MTA-STS and BIMI. Learn which records are mandatory versus optional and the exact order to add them so nothing breaks mid-setup, then confirm each one with a free scan.
What Is a DNS TXT Record? A Plain-English Guide for Email Authentication
A DNS TXT record stores plain text in your domain's DNS, and for most people the only reason to touch one is email authentication: SPF, DKIM, and DMARC all live in TXT records. This guide shows annotated real examples, explains the host, value, and TTL fields, and covers the 255-character split and multiple-strings gotchas that quietly break records.
550 5.7.1 'Email Rejected Per DMARC Policy': Causes and Step-by-Step Fix
A 550 5.7.1 email rejected per DMARC policy bounce means the receiving server enforced your p=reject or p=quarantine policy because the message failed DMARC. This guide shows how to tell whether it is your own mail or a forgotten third-party tool, how to read the bounce, and how to add the missing SPF include or DKIM key instead of weakening your policy.
550 5.7.23 'SPF Validation Failed': Why It Happens and How to Resolve It
The 550 5.7.23 bounce means the receiver rejected your mail because SPF authentication failed and a policy told it to reject. It usually points to one of three things: a hard -all fail from a sender that is not listed, an SPF PermError from too many DNS lookups or broken syntax, or forwarding that rewrites the path. This guide separates the three causes and shows how to confirm which one you have.
How to Check Your Email Deliverability: A Free Step-by-Step Audit
Check your email deliverability for free by running the checks in the order a pro would: authentication with our scanner first, then blocklist status, a real seed and inbox-placement test, Google Postmaster Tools and Microsoft SNDS reputation, and finally content and spam scoring. This audit gives you a full inbox-placement picture without paying for a suite.