Some upsetting parliamentary form of communication (5)
I believe the answer is:
'form of communication' is the definition.
(I know that email is a type of message)
'some upsetting parliamentary' is the wordplay.
'upsetting' says the letters should be written in reverse.
'some' indicates a hidden word (some of the parts of the word are used).
'liame' can be found hidden inside 'parliamentary'.
'liame' in reverse letter order is 'EMAIL'.
(Other definitions for email that I've seen before include "Send one online" , "Electronic communication" , "Internet-borne communication" , "Digital message" , "Message sent via computer" .)