EmailLabs says it’s time for B2C marketers to throw out their old templates and replace them with longer, narrower versions.

The betas of both Yahoo’s and Microsoft’s online e-mail clients enable the preview pane by default but these spaces are much smaller than what consumers were hitherto used to. Hence, e-mailers are advised to put calls-to-action and other critical information at the top of messages.

Due to widespread adoption of Microsoft Outlooks preview-pane
function in corporate settings, B-to-B marketers have been dealing with
this design challenge for some time. Not so for B-to-C marketers, who
until now could safely assume that most consumers would see their
entire emails as designed.

"B-to-C marketers who want big results had better start thinking
small," said Stefan Pollard, the company’s director of consulting
services. "Many are completely unaware that preview panes and
automatically blocked images can make their current design templates
virtually unreadable. If they were to use a third-party rendering tool
to actually test how their e-mails look in consumers’ inboxes, they
might be shocked."

Preview Panes and Image Blocking by Major Web-Based Email Clients:

(a) Email Client in beta mode — settings may change with full release

More reasoning is in this press release.

Source: ClickZ