I’m a fan of valid HTML code on websites and definitely don’t care for HTML in e-mail messages. In fact, once I’ve filtered out known senders and mailing lists then the presence of HTML in an e-mail adds points for the likelihood of an e-mail being spam or otherwise unwanted junk.
I had no idea though that some services filter emails to the junk based on whether or not the HTML coding in the e-mail meets standards for coding. digg pointed me towards this ClickZ report which came up with some startling information.
Using outdated or incorrect code is a major reason why e-mail to domains such as MSN/Hotmail and AOL are blocked or delivered to bulk or junk mail folders.
You may think you don’t have to worry about this. Your e-mail may render correctly and look just fine to you. Wrong! Pivotal Veracity, a delivery-monitoring service provider, estimates nearly 100 percent of all HTML e-mail doesn’t comply with World Wide Web Consortium (W3C) standards.
Because each ISP handles e-mail differently, messages that get past the filters at one destination may be filtered or entirely blocked at another. Why are some ISPs so concerned about HTML code? You can thank spammers, of course. HTML syntax and format errors are common tricks spammers use to foil standard content filters.