Answer:
There are formatting issues in the closing.
Explanation:
Email is the most used device for correspondence between the employer and the employee or generally when we write to someone who has authority. It consists of a subject (exposing the main purpose of the email, it is important to be clear), salutation(greeting), body (where we explain the purpose a little bit more detailed, but still not exaggerating with details) and closing greeting.
Greetings are very formal and prescribed. Salutation starts with Dear... the rest depends on who are we talking to, we can refer to title or name.
Dear Mr. Jackson
Closing salutation also matters, usually we do it by writing Sincerely and our name.
Sincerely,
John Smith
So, what Serena did here is that she included a preposition from between Sincerely and her name, which is something that shouldn`t be done.
