Domainkeys identified mail (dkim) defines a domain-level authentication framework for email using public-key cryptography and key server technology to permit verification of the source and contents of messages by either mail transport agents (mtas) or mail user agents (muas).

libdkim is a library, developed by alt-n technologies, that allows incorporating dkim into an existing mta or other application. it provides full support for signing, verifying, and ssp. see the changelogs for information on compliance with specifications.