Answer mail left by eastern early Christian (7)
I believe the answer is:
apostle
'early christian' is the definition.
(follower of Jesus)
'answer mail left by eastern' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'mail' becomes 'post' (synonyms).
'left by' becomes 'l' (I've seen this in other clues).
'eastern' becomes 'e'.
'a'+'post'+'l'+'e'='APOSTLE'
(Other definitions for apostle that I've seen before include "Thaddeus, perhaps" , "A follower of Jesus" , "To lapse (anag) - ardent supporter of a cause" , "E.g. St Paul" , "John, perhaps" .)