Reading about mojo mail, one useful extension requires the host to support an email alias pointing to a script. Will that work here?
Not easily, but you can work around this by piping to the script from procmail (see the procmail article in kbase).
Alternately, you could use a shell / ftp user that doesn’t receive any other mail and pipe the the script in a .forward file (it has to be named .forward.postfix). Then send mail for the address you want to that user.
That seems reasonable. Thanks!