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Why Bother With Plain-Text Emails?
http://cdemails.com/articles/3512/1/Why-Bother-With-Plain-Text-Emails/Page1.html
Mailchimp Resource Center
MailChimp, a leading do-it-yourself email marketing service, provides tools to over 15,000 small businesses, design agencies, non-profits, restaurants, and e-Commerce organizations worldwide. Customers can create professional, eye-catching HTML emails in minutes with easy-to-use web based tools.  
By Mailchimp Resource Center
Published on 08/31/2008
 
These days, just about all email programs can render HTML email, and sooo many people have high-speed Internet connections. So we see a lot of marketers ignoring the plain-text field. This is a mistake.