There are two formats that emails generally use: plain text and HTML. Many email clients will have an option to switch between the two modes. Here's what happens when you use either of these formats in Mail-to-Blogger:
Plain Text: Everything is published on your blog exactly as you type it. That is, entering
<strong> in your post will not make text bold. The
<> brackets will be escaped and your published blog will actually display
<strong> as text.
HTML: All HTML is interpreted as HTML. If you use your email client's formatting functions to make text bold, you may not see the
<strong> tag, but it will be included in your post and the text will appear bold on your blog. If you want to enter code manually, you may need to use an "edit source code" mode or something similar in your email client.