Email Beginnings
If you were writing your instructor (me, Allisson Diego dos Santos) an informal email, you could start with just "Julia,". If you hadn't met me before but wanted to email me, what would be the best opening?
Dear Mr. Santos
If you were writing me (Allisson Diego dos Santos) to ask an upcoming lesson, why would "Hello" or "Hello Diego" be a bad subject line (title)?
It doesn't explain the reason you are writing me or who you are. If you are writing an instructor, the name and time of the class would be appropriate. For example: Re: 10:30 AM English Class next Wed. Also, a more specific subject line makes sure that the message isn't mistaken for spam, or simply ignored.