Change from HTML to Plain Text in Outlook
Found on Wired on Tuesday, 17 November 2009

A complex HTML e-mail will in all likelihood still look very different when viewed in Outlook and Gmail. Images do not display properly, tables become larger or have unexpectedly thicker borders, hyperlinks in image maps are in the wrong location or missing entirely; quite frankly, it's embarrassing.
Although HTML 5 and Flash on mobile devices has some exciting potential for the future of e-mail, it's nice to know that you can always fall back on plain text to make sure e-mail does what it was designed to do: get your message delivered.
And they always have that spammy touch too. Displaying HTML e-mails and especially creating them, are the first things that should get disabled in any e-mail client installation.