Newsletter design is not a science but an art itself: It has to be rendered in countless email clients with poor HTML support; it must lots of information in such a small space and, last but not least, it has to engage the audience in just a couple of seconds before the email is disregardded or even marked as spam.
Conforming to these constraints requires the overall newsletter layout to keep a balance between shiny design and fast user engagement. The code delivered needs to deal with legacy XHTML standards and extreme care must be driven in the code in order to ensure it will not be flagged as SPAM by the email delivery system.
On a side note, any newsletter layout should be easily editable by the company marketing representatives. On 2011 I was approached by a longtime client by that time, Camping La Marina, who was in need of a customizable newsletter design. After doing somre research on the company's marketing requirements, we agreed on a design featuring a main area with a CTA link, 3 secondary links/items and 3 third-level slots, being all of them fully customizable by the client. We used MailChimp and its terrific customisation tools to deliver a fully customizable template that serve as teh foundation to several succesful email campaigns during 2011 and 2012.
The screenshot below is a good sample of how customisable was the design displayed above. Most of this functionality was handled by the MailChimp editor and could be easily managed by any non-technical individual at the company.