Unacceptable corollaries for mounted escorts (9)

I believe the answer is:

outriders

I'm a little stuck... Click here to teach me more about this clue!

'escorts' is the definition.
(I know this)

'unacceptable corollaries for' is the wordplay.
'unacceptable' becomes 'out' (out can mean incorrect or inappropriate).
'corollaries for' becomes 'riders' (I can't explain this - if you can you should believe this answer much more).
'out'+'riders'='OUTRIDERS'

'mounted' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.

Can you help me to learn more?

(Another definition for outriders that I've seen is " Bodyguards".)

I've seen this clue in The Times.

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