I'm of the belief that email is meant for mostly pretty concise and purposeful communication. I honestly will only skim through an excessively long email. Oftentimes the formatting is irregular because emails sometimes just do that, so reading a long email can be a bit difficult.

If I need to send something of length, particularly something that is really its own text (i.e. a journal entry, a reflection, a piece of creative writing, etc.), I write that document in a Word or Google Doc and attach the file to the email. Then, the email is simply an explanation about what the attached file contains and what I am requesting the receiver to do in regards to that document.