Page checked by very severe correspondent (3,3)
I believe the answer is:
pen pal
'correspondent' is the definition.
(pen pal is a kind of correspondent)
'page checked by very severe' is the wordplay.
'page' becomes 'p'.
'checked by' is an insertion indicator.
'very severe' becomes 'penal' (I've seen this before).
'p' inserted inside 'penal' is 'PEN PAL'.
(Other definitions for pen pal that I've seen before include "Mail friend" , "American friend via correspondence" , "Friend you know only through correspondence" , "Friend who communicates in letters" , "A friend who communicates through correspondence" .)