Skip to content
Spaw
Get your API key

DKIM

published · September 13, 2026

DKIM (DomainKeys Identified Mail, RFC 6376) is a signature a sending server adds to a message, verified by the receiver against a public key the domain publishes in DNS under a selector.

DKIM, DomainKeys Identified Mail, is the mechanism of RFC 6376 by which a sending server signs a message with a private key and the receiver verifies the signature against a public key the domain publishes in DNS. The signature covers chosen headers and the body, so a message that is altered in transit, or that merely claims a domain it was never signed by, fails verification.

What Spaw answers

The domain endpoint reports dkim_selectors: which of the common selector names publish a key under <selector>._domainkey.<domain>. An empty list means none of the common names answered, which is not the same as no DKIM at all — a domain may sign under a selector nobody else uses — and null means the lookups failed. The free DKIM checker reads the same list.

What it does not mean

A published key proves the domain can sign, not that a given message was signed or that the signature aligned with the visible sender. DMARC is the policy that ties DKIM and SPF to the address a person sees.

Related

markdown version: /glossary/dkim.md

Verify addresses the same way

The Spaw API runs every check described here on each lookup, with an SMTP handshake that never sends mail. 10 free lookups a month, no card required.

Get your API key

More glossary

  • Area-code overlay

    An area-code overlay is a new area code added over the same area as an existing one, instead of splitting it, so neighbours can hold different codes and local calls need ten digits.

  • Calling window

    A calling window is the span of local hours a sender contacts people in. Spaw answers in_call_window from the number's time zones: clock arithmetic, not compliance advice.

  • Fictional number

    A fictional number sits in a range kept out of service for films, TV and other fiction: 555-0100 to 555-0199 in North America, and ranges Ofcom, ARCEP, ACMA and ComReg reserve elsewhere.

  • International (exit) prefix

    An international prefix is what is dialled to leave a country before the calling code: 00 in most of the world, 011 in North America. Spaw reads it and suggests a fix in did_you_mean.

  • International network number

    An international network number sits under a calling code the ITU gives a global service rather than a country, such as +870, +881, +882 or +883, so its country is null.

  • Live carrier check (HLR lookup)

    A live carrier check asks the mobile networks, at the moment of the lookup, whether a number is in service, which network serves it and whether it is roaming. On Spaw it is not enabled.

  • Number pooling (thousands-blocks)

    Number pooling splits a North American central office code into ten blocks of a thousand numbers, each assigned to a carrier separately, so one code can hold several carriers' numbers.

  • Number portability

    Number portability lets a subscriber keep a phone number when changing carrier. The number's block stays listed under the carrier it was issued to, so block data names the original holder.