One blocking fake e-mails causes discomfort (7)
I believe the answer is:
malaise
'discomfort' is the definition.
(malaise is a kind of discomfort)
'one blocking fake e-mails' is the wordplay.
'one' becomes 'a'.
'blocking' is an insertion indicator.
'fake' indicates anagramming the letters (I've seen this in other clues).
'e'+'mails'='emails'
'emails' anagrammed gives 'mlaise'.
'a' inserted into 'mlaise' is 'MALAISE'.
'causes' is the link.
(Other definitions for malaise that I've seen before include "Feeling of impending illness" , "Unease; lethargy" , "Feeling of illness or mental uneasiness" , "General feeling of unease or illness" , "Disquiet" .)