You must never write "i" when you mean "I". It makes you look LAZY. Too lazy to press the shift key while pressing the "i" key. Even in email you must write properly as if you were trying to impress an editor.
This looks like a tiny thing. It is not. The capital "I" for the word meaning yourself is one of the first rules of written English, and an editor reads a lowercase "i" as a flashing sign that says: this person does not care. If you cannot be bothered with the easiest rule of all, why would an editor trust you with a difficult story?
The same goes for the start of every sentence. A capital letter at the front, a full stop at the end. Names of people, places, papers and brands all take capitals too: Sydney, the Herald, Tuesday, Qantas. These are not decorations. They are the road signs that tell the reader where one thought ends and the next begins.
I know the habit comes from texting and quick messages, where people drop their capitals to save a second. But you are not texting a mate. You are trying to convince a busy professional to pay you money and print your name. Write every email, every note, every caption as if the toughest editor in town is reading it, because one day one of them will be.
Press the shift key. It takes a fraction of a second, and it tells the world you are a professional.