MTA - rewrite from and to based on subject tag

I want a windows program that will act as an SMTP relay with the standard set of features (like relay restriction etc...) but with the ability to re-write the "FROM" and "TO" fields based on a message subject. E.G an incoming email sent to companya@[login to view URL] will be relayed through this software then the TO will be changed to: person@[login to view URL] and the subject tagged with [!--companya--!] an outbound email sent from person@[login to view URL] will be relayed through the software and if the subject contains a tag: [!--companya--!] then the FROM address will be changed to companya@[login to view URL] and the subject tag removed. The software can be an extension to IIS SMTP (preferably 7.0) services or stand alone.