Emailology is a website which aims to guide designers and developers with the best practices of e-mail design.

The project includes an e-mail boilerplate, that is very well-commented and includes hacks for cross-client compatibility, for starting quickly.

A knowledgebase lists the tips and tricks categorized for each e-mail client. It is the right place for finding answers to client-specific issues.

There is a standards guide which presents the universally-supported HTML and CSS tags (it is possible to get client-specific data).

And, a character conversion feature allows copy-pasting your own code for converting the special characters into HTML entities.

E-mail code validation is a painful job considering many e-mail clients/applications have a low-level HTML-CSS rendering support and many others have their own standards. Actually, it is worse than designing for the browser.

Fractal is a free-to-use web application for validating HTML-CSS code across 24 most-popular e-mail clients.

It simply works by pasting the code to the application and finding out if each line is validated, if not, why and in which e-mail clients.

Best of all, Fractal doesn't come with only the bad news but also suggests fixes.

P.S. Besides the desktop and web-based e-mail applications, it also checks the code for the mobile as well.

There are various new and exciting stuff with the website development like HTML5 and CSS3.

But, when it comes to designing HTML e-mails, it is still the tables and hacks for improving compatibility with different e-mail clients.

HTML E-mail Boilerplate is a project which presents a starting point for HTML e-mail design and includes solutions for the major rendering problems with the most common email clients.

The code is very well documented and the download pack includes a non-documented version).

CampaignMonitor, an e-mail marketing service, is sharing 100+ professional, good-looking and free HTML e-mail templates.

They are created by several talented + well-known designers and come with the PSD source files for total customization.

All templates are tested in 20+ e-mail applications including the popular ones like Outlook 2010, Gmail, Lotus Notes, Apple Mail and iPhone.

MailChimp presents 4 free HTML e-mail templates that are well-optimized for most of the e-mail applications.

Templates include a basic newsletter, postcard and 2-column designs.

You can also find newsletter coding tips at the same address and a free e-mail marketing e-book which covers email marketing benchmarks (average open/click rates, bounces, unsubs), how spam filters work & more.

Getting your email to look great in all the major email clients can be a challenge at times, so, Campaign Monitor done the hard work for you with these 30 free e-mail templates.

They’ve tested them in all the major email clients, so add your own content and you’re all set.