How to run procmail in cmdline and provide .eml file as input?

Procmail failed while running my external python script on received email. After that I tried run that script manually and provide the same arguments as procmail - it passed without any problems, so I'm trying to figure out why procmail had problems with that script. Is is possible to run procmail from cmdline and provide path to saved .eml file with email's raw data? Shall I configure something else, maybe permissions are wrong - but I guess procmail is executed by the same user as I did a manual check on python script.