DKIMproxy is an SMTP proxy that implements the DKIM and DomainKeys
standards, to sign and verify email messages using digital signatures
and DNS records. It can be used to add DKIM support to nearly any
existing SMTP mail server. It comprises two separate proxies, an
"outbound" proxy for signing outgoing email, and an "inbound" proxy for
verifying signatures of incoming email.

Homepage:
https://dkimproxy.sourceforge.net/
