Jump ship with a ring on one's letters (7,4,4)

I believe the answer is:

abandon ones post

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'jump ship' is the definition.
I know nothing about this answer so I can't judge whether this works.

'with a ring on one's letters' is the wordplay.
'with' is an insertion indicator.
'a' becomes 'one'.
'ring on' becomes 'abandons' (I am not sure about this - if you are sure you should believe this answer much more).
'one's letters' becomes 'post' (someone's mail).
'one' inserted inside 'abandons' is 'abandonones'.
'abandonones'+'post'='ABANDON ONES POST'

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I've seen this clue in the Sydney Morning Herald.

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