It's not correct. The correct sentence could be: "It's great to hear that you liked the email."

It is not redundant, it is wrong and doesn't belong in the sentence. The sentence means, that the speaker finds it great knowing and hearing that the other liked the email. So 'you' doesn't really belong in the context, unless you mean something else and still it won't be expressed this way.. The correct sentence is: "It is great to hear, you liked the email."