selectordomainkeydomain

Selectordomainkeydomain is a shorthand used in some technical texts to refer to the DKIM-related identifiers that enable publishers and recipients to locate and verify a DKIM public key in DNS. The term is not an official standard, but it helps describe the interplay between the selector, the signing domain, and the DNS location of the public key.

In DKIM, an email is signed with a private key associated with a specific signing domain (the d= domain). The recipient uses a DNS lookup to retrieve the corresponding public key, by querying a TXT record named using the selector and the domain: selector._domainkey.domain. The selector is an arbitrary label chosen by the domain owner to identify a particular key or signing policy; the domain is the signing domain that appears in the DKIM signature as d=; the key domain refers to the DNS zone where the public key is published.

DNS record format for the public key is a TXT record at the constructed name, containing values such as v=DKIM1; k=rsa; p=BASE64VALUE. The value specifies the DKIM version, key type, and the base64-encoded public key. A successful lookup allows the recipient to verify the DKIM signature attached to the message header.

Usage and verification flow involve the signer attaching a DKIM signature to outgoing mail, and the verifier retrieving the public key from selector._domainkey.domain to validate integrity and authenticity. Best practices include rotating keys periodically, publishing accurate keys in DNS, and testing configurations with diagnostic tools. See also DKIM, DNS TXT records, and DMARC.