Use In-line CSS styles. Always use in-line CSS styles rather than classes. For more information on CSS support in emails, check out this Guide to CSS Support in Email.
Use Basic HTML Tables. To have your email blast work across the many different email browsers and clients, use basic HTML tables. Most of the complicated code that works on websites does NOT work in an HTML blast. For example, divs and shortcodes do NOT work at all in certain email browsers.
Don’t Use Coding Shortcuts. For example, when styling CSS, set each property rather than grouped in one shortcut code (i.e. use “border-width:5px; border-style:solid; border-color:#000000;” rather than “border: 5px solid red;”). For both HTML and CSS, use all 6 hexadecimal numbers instead of just three for a shortcut (#ffffff and #000000 would be correct, rather than #fff and #000).
Avoid Colspans. When building your blast with tables, avoid using colspans (column spans that show up as colspan=””) as it usually renders differently for each email client and could “break” your blast.
Test Your Blast. Be sure to check and test your blast before you submit. All submissions should be final artwork.