It will likely perform as bad as Micheal Jackson on his return concerts.
The command line scanner will work, but only for a small volume of emails.
If you can purchase or use a scanner that integrates better with Mailmarshal. then you will have much better performance.
All that aside - If you want to use it, then you probably want to create a batch file which downloads the latest zip file from here: ftp://ftp.mcafee.com/pub/datfiles/english/ each day and copies it into the directory where the engine resides.