A day to correspond will be enough (8)
I believe the answer is:
adequate
'enough' is the definition.
('adequate' can be a synonym of 'enough')
'a day to correspond' is the wordplay.
'a day' becomes 'ad' (I've seen this in other clues).
'to correspond' becomes 'equate' ('equate' can be a synonym of 'correspond'**).
'ad'+'equate'='ADEQUATE'
'will be' is the link.
(Other definitions for adequate that I've seen before include "Fair to middling" , "Sufficient or all right" , "Enough to meet a purpose" , "up to the job?" , "Just about sufficient, acceptable" .)