WordPress will use the Subject line of your email for the title of the post, and all body of the email will be used as the content of the post, with common HTML tags stripped. WordPress will file the post under whichever category is selected for “Usual Category” in Step 1, and will use Site Admin as the poster.
Any images and attachments in your email will be posted inline.
However .. on one of my blogs I have a Vlogger doing videos and we wish to just email the YouTube code directly to the blog for posting. It’s stripping the <object> and html for the code for the YouTube.