"Can we also give feedback by email ?"
Managers in Asia struggle with giving feedback, in particular the feedback for improvement. The fear of "what the discussion will lead to" very often simply means that managers avoid addressing the issues, and the team members don't get the feedback that would allow them to do better. Issues remain unsaid for way too long until they reach crisis proportions, and then it becomes easily an end-of-employment discussion. Lose-lose for sure.
So now it seems that (maybe) some have found a solution: feedback by email !! After all, they must be thinking it is better than avoiding giving feedback all together, and sending out a feedback email means they can 'tick' this off of their to-do list. "Oh yes, I did give him the feedback ...!". There is nothing so easy to ignore as an email. And sending an email tells a lot about the effort the manager is willing to put into this ... The medium IS the message.
So no, giving feedback for improvement does not happen by email. Muster the courage to have a face-to-face conversation. Get comfortable (before you start) with the fact that the conversation will probably not turn out exactly as you have in mind. And keep in mind, whichever way the conversation goes, that your target is a win-win solution. Finally, don't forget that this is a conversation, so catch yourself when you become aware you are the one doing all the talking: ask a question, shut it and listen.