I love OS X's App - Notes which is super light and amazing app. It lets you write notes ( with images, text formatting is allowed, tables too).

Interestingly when you sync your Email account such as Gmail's, it saves your notes in the form of e-mail ( it basically emails you the note's content ).

Now, this could be useful as you will have backup of your notes but it can creep out a lot of people.

Therefore, save your notes in the "On my Mac" section which can be chosed from Notes ( Top left corner ) and select "On My Mac " Account.

Observation -

It didn't delete the email note even when I deleted the notes which was very annoying.

Good luck with using your Notes App.