Marco Balmer wrote:

Their AntiVir Unix MailGate works with Sendmail's milterlib. Courier has more or less the same callbacks, however the details are slightly different.

One may try implement milterlib for Courier. It provides for callbacks on connection (not provided by Courier, should be faked), helo (ditto), envfrom (ditto), envrcpt (provided as rcpt APIs), header (not provided for each header, can be forwarded by a global filter), eoh (ditto), body (ditto: Courier does not split messages into header/body parts), eom, abort, close.

In addition, the socket can only be a unix domain socket and must be in specific Courier directories. Forwarding to a different socket for library interface compliance is a gratuitous waste of resources.

Presumably, AntiVir is really only interested in the body of the message and just the MIME headers necessary to parse it. A small subset of the milterlib possibilities. Thus, it would be easier and better to implement that directly using the global filtering API.

Unfortunately, AntiVir is not available as a library. Instead, they support each single MTA. Hence, support for Courier should be coded by their staff. Perhaps, they would grab some startup approach from my interface for SophosAV http://www.tana.it/sw/avfilter/