Such messages mostly mislead criminal (6)
I believe the answer is:
emails
'such messages' is the definition.
(electronic messages)
'mostly mislead criminal' is the wordplay.
'mostly' means to remove the last letter (most but not all of the word).
'criminal' indicates anagramming the letters.
'mislead' with its final letter taken off is 'mislea'.
'mislea' with letters rearranged gives 'EMAILS'.
(Other definitions for emails that I've seen before include "Computer communications" , "Electronic communications" , "Electronic messages" .)