Suppose the mail is delayed after you are reported? (9)
I believe the answer is:
postulate
'suppose' is the definition.
(thesaurus)
'the mail is delayed after you are reported?' is the wordplay.
'the mail' becomes 'post' ('post' can be a synonym of 'mail').
'is delayed' becomes 'late' (I've seen this before).
'after' says to put letters next to each other.
'are reported?' indicates a 'sounds like' (homophone) clue.
'you' is a homophone of 'u'.
'late' put after 'u' is 'ulate'.
'post'+'ulate'='POSTULATE'
(Other definitions for postulate that I've seen before include "Assume as axiom" , "Let sap out in order to claim something" , "Put forward" , "Suppose" , "Take for granted or lay down as self-evident" .)