New issue by Anachron on mblaze repository

https://github.com/leahneukirchen/mblaze/issues/204

Description:
It would be handy if `mcom` supports to call a program with the filename of the sent mail.
That way, I can check the headers and run hooks depending on what I find. 

It would either need to be included [here](https://github.com/leahneukirchen/mblaze/blob/master/mcom#L443) and [here](https://github.com/leahneukirchen/mblaze/blob/master/mcom#L461) or [here](https://github.com/leahneukirchen/mblaze/blob/master/mcom#L475).