default prefix is [*EXT*] if not specified on the CLI
default extraprefix is [EXT] if not specified on the CLI
Be warned that a too generic prefix could match legitimate wording and thus it won't be added to the Subject
option --encode forces prefix encoding whether the subject is encoded or not.
Known limitations
if Subject is too long and spans between multiple datalines, only the begining will be analyzed for prefix token
RFC2047 Subject won't be decoded if 1/ happens inside an encoded string