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DNS Domain Detective

Find DKIM keys, CNAMEs, SPF and DMARC for any domain. Open DNS Domain Detective

• How to find the DKIM selector for your domain
  A DKIM record sits under a selector name that can be almost anything. Why that makes it hard to find, and how to track it down.
• What is SPF? A plain explanation for domain owners
  SPF is a public list of the servers allowed to send email for your domain. How it works, what usually goes wrong, and how to check yours.
• What is DMARC? A plain explanation
  DMARC tells receiving servers what to do with email that fails SPF and DKIM checks, and asks for reports. How it works and what the record looks like.
• What is a CNAME record and when is it used?
  A CNAME record makes one name an alias of another. How it works, the main rule about it, and where CNAMEs usually show up.
• What is an MX record? How email finds your mailbox
  MX records tell the world which servers receive email for your domain. What they contain, how priority works and what usually goes wrong.
• DMARC policies: none, quarantine and reject explained
  The p= value in a DMARC record is the policy. What none, quarantine and reject mean for email that fails the check.
• How do I check the DNS records of a domain?
  Look up A, MX, TXT and NS records with a command-line tool or an app. What to ask for and how to read the answer.
• What is a TXT record used for?
  A TXT record stores text in DNS. SPF, DKIM, DMARC and ownership checks all rely on it. How it works and what the limits are.
• Why does my email go to spam? Start with authentication
  Email can land in spam for many reasons. Missing or broken SPF, DKIM and DMARC records are among the ones you can check and fix yourself.
• SPF, DKIM and DMARC: what is the difference?
  SPF lists allowed servers, DKIM signs messages, DMARC sets the policy. How the three differ and how they work together.
• SPF 'too many DNS lookups': what it means
  An SPF check may cause at most ten DNS lookups. What counts, why includes add up quickly, and what happens when the limit is passed.
• SPF ~all vs -all: softfail or fail?
  The ending of an SPF record says what to do with servers that are not listed. What -all, ~all, ?all and +all mean.
• What are name servers (NS records)?
  Name servers are the servers that answer DNS questions for your domain. Where they are set, why there are usually two or more, and what changing them does.
• What is TTL in DNS, and how long do changes take?
  TTL is the number of seconds a DNS answer may be cached. How it affects how quickly changes show up, and what 'propagation' really means.
• What does a DKIM record look like?
  A DKIM record is a TXT record under selector._domainkey. See its parts: v=DKIM1, the key type and the public key, and what a CNAME version means.
• Why does DKIM fail? The common causes
  A DKIM check can fail for a handful of reasons: a missing record, a wrong selector, a changed key or a message altered after signing.
• Do subdomains need their own SPF, DKIM and DMARC records?
  DNS records belong to one name. How SPF, MX, DKIM and DMARC behave for subdomains, and what the sp= tag in DMARC does.

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