If you're interested in a more precise reason, what you're seeing is almost certainly a side-effect of poor handling of a quirk of the
standard email format:
There are two limits that this standard places on the number of characters in a line. Each line of characters MUST be no more than 998 characters, and SHOULD be no more than 78 characters, excluding the CRLF.
The problem is that many programs that send email in HTML format--which, based on the chopped-in-half yours does--just toss in those breaks wherever they occur. (Keep in mind that a line break, when part of an HTML document, just looks like a space when displayed.)
I get one HTML email newsletter that will periodically have words with weird space in the middle due to this issue. In your case, your editor is using an entity to insert a non-breaking space, but that fell across the 998 character max-line-length and got cut in half, so that you just saw two pieces of the raw code. I forget why, technically, the ! becomes visible, but it's a side-effect of the same problem (again, I've seen it produced by form-to-email scripts every 998 characters).
Solution-wise, the question is already answered: If it's a press release, either format it as plain text, or attach a PDF if you're married to your layout and/or want to include graphics.
[Addition: An alternate solution is apparently switching the message encoding to base-64, if that's an option in whatever mailer you're using. It will, apparently, encode the message such that the line length limitation is not a problem, so long as the mailer and receiver both support it.]