For the last few versions of Outlook, the setting to enable Word as the e-mail editor has been enabled by default. While some people like using Word as an email editor due to the advanced features available, others dislike it because of Word's tendency to generate a lot of HTML markup for even simple HTML mails. If you do want to use Word, you can minimize the amount of markup it adds as follows:
1. Open up Word
2. Tools | Options
3. On the General tab, select Email Options
4. Switch to the General tab
You'll see four main settings:
4. Rely on CSS
I did some very unscientific tests using this text as a sample:
this has fancy formatting
and here are my results (this counts total message size, not just size of the HTML bodypart):
Not using CSS: None=11KB, Medium=8KB, High=6KB
Using CSS: None=9KB, Medium=7KB, High=5KB
All of the items displayed properly on receive using Outlook. You're probably safe using the "High" setting as long as you don't use Word-specific features like the drawing tools in your messages. Stick to basic text formatting and inline pictures.
P.S. I do love HTML for email, regardless of size or "bloat". It's particularly useful in long threads in combination with the "Mark my comments with" setting in Outlook.