Formal character used in mail for dispatch (10)
I believe the answer is:
impersonal
'formal' is the definition.
(thesaurus)
'character used in mail for dispatch' is the wordplay.
I cannot quite see how this works, but
'character' could be 'persona' (synonyms) and 'persona' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for impersonal that I've seen before include "Cold" , "Cool" , "Objective; disinterested" , "Ignoring one's own feelings" , "Aloof" .)