Feedback at Work Causing Frustration

My boss has given me autonomy to answer emails, but sometimes when I do, he gives me feedback that I should answer them differently. I feel like not answering emails anymore every time this happens.

I feel incompetent and I DESPISE feeling incompetent. It has happened several times and I don’t like how I react. I want to appreciate the feedback instead of getting defensive because I feel incompetent. Any ideas?