Parameter and Command Reference > Connector Framework Server Parameters > Import Service Parameters > ImportFamilyRootExcludeFmtCSV 

ImportFamilyRootExcludeFmtCSV 
Specify which KeyView formats not to designate as family roots if family hashing is enabled. For example, if you exclude the PST format (KeyView value 356), when Import Module Advanced hashes a PST file, it does not consider PST container as the root format. Instead, it searches for a deeper format that is not listed as a CSV: in this case, it would find the MAIL format, which would then be considered the root of the family.
For a complete list of KeyView formats, see KeyView Format Codes.
 
356=PST
157=ZIP
233=EML
345=MSG