Former partner blocks dry electronic message (4)
I believe the answer is:
text
'electronic message' is the definition.
(I've seen this before)
'former partner blocks dry' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'blocks' indicates putting letters inside (the inside letters form a 'blockage').
'dry' becomes 'tt' (short for teetotal - no alcohol).
'ex' inserted inside 'tt' is 'TEXT'.
(Other definitions for text that I've seen before include "Printed or written words" , "Words of something printed" , "Wording" , "Printed matter" , "Main body of book or page" .)