Okay.
For pasting into the body of the e-mail, you can't format as you would for a manuscript, and they don't expect you to. So don't bother to try.
You paste it in single-spaced, with one extra return between paragraphs. Also, no indenting of the first line. The easiest way to do this is to copy the pages from your manuscript and paste into a new file, then change the formatting of the new file. That is, globally change one return to two returns, change smart quotes to straight quotes if you used smart quotes, left-align any centred headings, and get rid of your first-line indenting. Then copy this new version into the body of your e-mail.
At this point in time, most e-mail clients will correctly display italicised text in italics, but if you want to be extra-specially sure, you can always put an underscore at the beginning and end of the italicised text, _like this_. Most editors will understand what the extraneous underscores are and won't be bothered by them even if they're unnecessary.
I also change the font to a sans serif one, since sans serif is easier to read onscreen. If the editor decides to print your pages out, they'll reformat it all to their preference anyway.