Mail job (4)
I believe the answer is:
post
I believe this is a double definition.
'mail' is the first definition.
(I've seen this before)
'job' is the second definition.
(post is a kind of job)
(Other definitions for post that I've seen before include "Stake; appointment" , "employment" , "Prefix meaning after" , "Job - letters - stake in ground" , "Leave message online" .)