Porter collecting mail for preacher (7)
I believe the answer is:
apostle
'preacher' is the definition.
(I've seen this before)
'porter collecting mail' is the wordplay.
'porter' becomes 'ale' (I've seen this in other clues).
'collecting' means one lot of letters goes inside another.
'mail' becomes 'post' (I've seen this before).
'ale' enclosing 'post' is 'APOSTLE'.
'for' acts as a link.
(Other definitions for apostle that I've seen before include "Peter, perhaps" , "To lapse (anag) - ardent supporter of a cause" , "Divine messenger" , "'Matthew or Mark, say (7)'" , "Chosen disciple" .)