Letters sent going after job (4)
I believe the answer is:
post
'letters' is the definition.
(letters in the mail or post)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for post that I've seen before include "Upright - letters" , "Leave message online" , "Prefix meaning after" , "Member < to comment on website" , "Letters and parcels; job" .)