Mark and Jack are the recipients (6)

I believe the answer is:

target

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'mark' is the definition.
(synonyms)

'jack are the recipients' is the wordplay.
'jack' becomes 'tar' (both are informal terms for sailor).
'are the recipients' becomes 'get' (I can't justify this - if you can you should give a lot more credence to this answer).
'tar'+'get'='TARGET'

'and' acts as a link.

Can you help me to learn more?

(Other definitions for target that I've seen before include "Aim, objective" , "Something to aim for" , "Object to be attained by archers (or fund raisers?)" , "Object of attack" , "Aimpoint" .)

I've seen this clue in the Evening Standard.

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