Users who create templates in Outlook 2010 are discovering that the resulting messages are converted to plain text when sent using a SMTP server. (Users with Exchange servers are not affected.)
We have two solutions until this bug is fixed. I think the easiest fix is to save the design as Stationery instead of a template. The first time its used, select it from New Items, Email Message using… More Stationery but after that it will be listed at the top of the New Items, Email Message using… flyout. If you need to use a template, set the contact to always use rich text.
If you save the design as stationery, you’ll need to save it in HTML format in the Stationery folder under your user account so it will be listed in the Stationery picker. An easy way to access this folder when saving the template is to type %appdata% in the filename field and press Enter then browse to the Microsoft\Stationery folder.