As part of deploying a new Postfix-and-qpsmtpd based mail architecture at work, I have developed some qpsmtpd plugins and extended its native queue/smtp-forward plugin.
- filter/dkimsign: Signs e-mail using Mail::DKIM. There are a other dkimsign plugins out there but I wanted to take a stab at doing one myself.
- filter/header_whitelist: Possibly controversial, could break many things if misused. I wanted a way to clean up all the extra garbage version headers, etc added by the multitude of scripts and platforms generating email in our environment. If the mere existence of this plugin doesn't violate RFC2822 or e-mail best practices, certain configurations certainly would. Use with care.
- queue/smtp-forward: I have extended the stock plugin to support the Postfix XCLIENT verb. This allows a qpsmtpd to pass information about the client (their IP and HELO, in particular) which Postfix can then use for access control and/or logging. I'll try and submit this back upstream.
You can find the plugins at my GitHub page.