A mug one possibly sent out for (5)

I believe the answer is:

stein

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'a mug' is the definition.
(I know that stein is a type of mug)

'one possibly sent out for' is the wordplay.
'one possibly' indicates anagramming the letters.
'out' indicates putting letters inside.
'for' becomes 'i' (I can't explain this - if you can you should believe this answer much more).
'sent' with letters rearranged gives 'sten'.
'sten' enclosing 'i' is 'STEIN'.

Can you help me to learn more?

(Other definitions for stein that I've seen before include "Glass" , "German tankard" , "German earthenware beer mug" , "Beer-mug" , "Gertrude ---; US writer" .)

I've seen this clue in the Evening Standard.

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