Maybe I am a bit old-school already, but I like the sound of this news post:
Due to an increased network threat condition, the Defense Department is
blocking all HTML-based e-mail messages…
The JTF-GNO mandated use of plain text e-mail because HTML messages pose
a threat to DOD because HTML text can be infected with spyware and, in
some cases, executable code that could enable intruders to gain access
to DOD networks, the JTF-GNO spokesman said.
In an e-mail to Federal Computer Week, a Navy user said that any HTML
messages sent to his account are automatically converted to plain text.
If something needs to look pretty, put it in an attachment or link to the website inside the email body.