In African country I picked up a little post (4)
I believe the answer is:
'post' is the definition.
(I know that post can be written as mail)
'in african country i picked up a little' is the wordplay.
'in african country i' becomes 'iam' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'picked up' says the letters should be written in reverse.
'a little' becomes 'l' (abbreviation).
'iam' reversed gives 'mai'.
'mai'+'l'='MAIL'
Can you help me to learn more?
(Other definitions for mail that I've seen before include "Form of armour; post" , "Posted letters" , "Paper" , "some self-defence material" , "Post in America" .)