dkimproxy binary package in Ubuntu Precise i386

 DKIMproxy is an SMTP-proxy that signs and/or verifies emails, using the
 Mail::DKIM module. It is designed for Postfix, but should work with any mail
 server. It comprises two separate proxies, an "outbound" proxy for signing
 outgoing email, and an "inbound" proxy for verifying signatures of incoming
 email (administrators can decide if they want to run both, or only one of
 them). With Postfix, the proxies can operate as either Before-Queue or
 After-Queue content filters, and they also can be chained with content
 filter proxies like Amavis, which is the current default configuration of
 the package.

Source package