libdkim1d binary package in Ubuntu Focal amd64

 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.

Source package