Armour for the post (4)

I believe the answer is:

mail

I believe this is a double definition.

'armour' is the first definition.
(I know that mail is a type of body armor)

'the post' is the second definition.
(synonyms)

'for' is the link.

(Other definitions for mail that I've seen before include "Posted letters" , "letter?" , "Post or body armour" , "Dispatch - armour" , "some self-defence material" .)

I've seen this clue in The Irish News.

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