If you need to write HTML for an e-mail newsletter, you need to get into an HTML mindset of 10 years ago. Which means a LOT of what we'd call bad practice in the modern web context.
- use nested tables for layout
- define width on each cell, not on table or tr
- add all styles inline
- don't use floats
Read the whole article by campaing monitor: http://www.campaignmonitor.com/resources/will-it-work/guidelines/