I will block upturn in poor-quality communication (1-4)
I believe the answer is:
'quality communication' is the definition.
'e mail' can be an answer for 'communication' (I've seen this before). I am not certain of the 'quality' bit.
'i will block upturn in poor' is the wordplay.
'will block' indicates putting letters inside (upper walls off glass inside formal).
'upturn in' is a reversal indicator.
'poor' becomes 'lame'.
'lame' reversed gives 'emal'.
'i' placed inside 'emal' is 'E-MAIL'.
Can you help me to learn more?
(Other definitions for e-mail that I've seen before include "Correspondence sent via internet" , "Electronic missive" , "Message sent via computer" , "Electronic communication" , "Web post" .)