The email formatted newsletter is designed to provide a relatively concise,
introduction to the subject matter. The "more details" is where you would
insert your link to your website where you would have the full article...or
in your case, "the text that doesn't flow into the box". The goal of the
design is the email newsletter to be small in file size, quick to load,
quick to read, and quick to get the reader to click the "more details" to
read more on your website.
If you don't have a website, then you can just delete the more details, and
enlarge your text box to accommodate your content.
You should consider converting your newsletter to a PDF that you attach to
your email, especially as your newsletter grows larger. You will probably
find it easier, more dependable, have less complications and much smaller
file sizes.
A popular and free PDF tool:
www.primopdf.com
DavidF