A slim assortment of postal packages (5)

I believe the answer is:

mails

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'postal packages' is the definition.
The definition and answer can be both man-made objects as well as being plural nouns.
Maybe there's a link between them I don't understand?

'a slim assortment' is the wordplay.
'assortment' indicates anagramming the letters.
'a'+'slim'='aslim'
'aslim' with letters rearranged gives 'MAILS'.

'of' acts as a link.

Can you help me to learn more?

(Another definition for mails that I've seen is " Sends by post".)

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