Sailor’s secure? He might get the sack (6)

I believe the answer is:

postie

'he might get the sack' is the definition.
(a postman carries a sack of letters)

'sailor's secure?' is the wordplay.
'sailor's' becomes 'PO's' (petty officer).
'secure?' becomes 'tie' (tying is a kind of securing).
'pos'+'tie'='POSTIE'

(Another definition for postie that I've seen is " Mail deliverer (informal)".)

I've seen this clue in The Times.

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