Email is its own animal separate from the rules of the Web. As far as coding---well, email is basically back in the dark ages. And there are as many ways an email can be rendered by the various email clients as there are programs.
An email sent to a Yahoo address, for instance, can be viewed in different browsers, each browser will add different criteria---rendering spaces where spaces should not appear. The same happens to Gmail and Hotmail. And then there is the possibility that the email will be viewed on a phone---rendering links differently; for example a PDF will be downloaded instead of opened.
What this means is that each and every newsletter and email needs to be tested on a variety of browsers, mail processors, and devices. And this applies no matter what email client you are using to process your newsletters.
In addition make sure that you send tests to the major carriers like Comcast. There have been times when emails sent through to Comcast have gone undelivered with no trace or rejection sent for failure. Missing a good portion of your customers because of a fluke in Comcast's system is not the optimal results you want for your marketing campaign. And, again, each and every email should be tested. There have been times when an email program has been set and working for months when all of the sudden, seemingly for no apparent reason, Comcast's mail go undelivered.
So once you have that eye catching email---make sure it catches the eyes of all your customers---test, test, test.