I am looking for an MTA that will allow me (a script, really) to proactively manage it's send queue in response to status codes returned by the remote servers I am delivering to.

Basically, for each mail sent I would like to be able to react to the SMTP reply code returned by the remote server, ex. '250 OK', or to any error conditions like connection timeouts.

Additionally, I would like to be able to manage the send queue moving forward based on this information, e.g. 'example.com has timed out the last 5 connection attempts, so no longer queue mail for recipients @example.com'.

I am currently using postfix and perl to parse it's logs for this information, but I am playing a game of catchup that is prone to errors (out-of-order log entries etc.) and it's starting to get messy (some real ugly regexes ;).

I really don't want to reinvent the wheel and use some language's smtp library; i would prefer to use a proven/fast/reliable MTA. I am however open to suggestions if what I need just isn't possible.

Thanks for your help!