Admirable composition of best email (9)
I believe the answer is:
estimable
'admirable' is the definition.
('estimable' can be similar in meaning to 'admirable')
'composition of best email' is the wordplay.
'composition of' indicates anagramming the letters (I've seen this in other clues).
'best'+'email'='bestemail'
'bestemail' anagrammed gives 'ESTIMABLE'.
(Other definitions for estimable that I've seen before include "Deserving respect" , "highly regarded" , "worthy of deep respect" , "Worthy of great respect" , "Highly valued" .)