Where mail is sorted in Peru (4)

I believe the answer is:

lima

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

'in peru' is the definition.
('Lima' is part of 'peru')

'where mail is sorted' is the wordplay.
'mail' can be anagrammed to 'LIMA'.
Though, I'm not clear how the anagram is indicated.

Can you help me to learn more?

(Other definitions for lima that I've seen before include "Kind of bean" , "South American capital" , "Peruvian capital" , "Send mail out to S America" , "Edible bean; capital city" .)

I've seen this clue in the Evening Standard.

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