… forget it. I was about to write a long-winded answer, that you can use usual cli mail softare to fetch the eml or msg files (mails) and use the tool on them and then send the pdf to the printers (most printers use pdf internally). But then i remembered that this would be the perfect job for a python script.
But, uh, wouldn’t you better just save the mails instead of printing them? Environment and cost and so on.