Shows old clipping in mail (5)
I believe the answer is:
expos
'shows' is the definition.
(I've seen this in another clue)
'old clipping in mail' is the wordplay.
'old' becomes 'ex' (prefix meaning former or onetime).
'clipping in mail' becomes 'pos' (I can't justify this - if you can you should give a lot more credence to this answer).
'ex'+'pos'='EXPOS'
Can you help me to learn more?
(Other definitions for expos that I've seen before include "Public displays" , "International shows" , "International exhibitions" .)