HTML emails and CSS formatting will take a huge hit when Outlook 2007 starts taking up positions on millions of desktops, and email newsletter publishers will have to take some extra steps to ensure their creations render correctly. But even that isn't a guarantee against problems with that new email program.
There is a big change coming with Outlook 2007, which is only a couple of weeks away from a full consumer release. In the interest of security, Outlook 2007 will use the Word 2007 HTML parsing and rendering engine to display HTML emails, and not Internet Explorer.
It appears Microsoft wants to try and mitigate the threat to Outlook users that can arrive with a malicious message that exploits a condition in IE. Without IE accessible through Outlook, criminals can't attack an IE exploit through Outlook.
A side effect of the things Outlook 2007 won't be able to do includes delivering HTML emails as they have been created by their publishers. A post at the Site Point blog summarized how a lot of publishers are likely to feel:
Not only that, but this new rendering engine isn't any better than that which Outlook previously used-indeed, it's far worse. With this release, Outlook drops from being one of the best clients for HTML email support to the level of Lotus Notes and Eudora, which, in the words of Campaign Monitor's David Grenier, "are serial killers making our email design lives hell."
Microsoft's changes in Outlook 2007 will mean publishers have to validate their code, and craft their publications to suit the available validator. That tool only works with a few Microsoft products like SharePoint, Expression, and Visual Studio, and with Macromedia's Dreamweaver.