Do better to speak formally after email fails (10)
I believe the answer is:
ameliorate
'do better' is the definition.
('ameliorate' can be a synonym of 'better')
'speak formally after email fails' is the wordplay.
'speak formally' becomes 'orate' (I've seen this before).
'after' means one lot of letters go next to another.
'fails' indicates an anagram (a failed spelling).
'email' anagrammed gives 'ameli'.
'orate' after 'ameli' is 'AMELIORATE'.
'to' is the link.
(Other definitions for ameliorate that I've seen before include "Make (something) better" , "Make (a bad thing) better" , "Become better" , "seen to improve" .)