"A way of communicating tedium" Mail involved (10)
I believe the answer is:
multimedia
'a way of communicating' is the definition.
(I know that multimedia is a type of transmission)
'tedium mail involved' is the wordplay.
'involved' is an anagram indicator (involved can mean confusing or complex).
'tedium'+'mail'='tediummail'
'tediummail' is an anagram of 'MULTIMEDIA'.
(Other definitions for multimedia that I've seen before include "several channels" , "Mail tedium (anag.)" , "Way of presenting data" , "Using several means of communication" .)