So how much do you know about spam filters? You may be surprised how much detail each different filter is now reviewing:

Spam Assassin, Google-Postini, Barracuda Networks, MSN SNDS, Yahoo Spam Guard, Email2pop, Sender Score, Cloudmark, Ironport

There is a whole section dedicated to specifics and types of spam filtering within Wikipedia’s pages. And what you don’t know about Bayesian Spam Filtering, could get your marketing email sent to the spam/bulk folder’s at your client’s ISP. Just a few examples to look for:

Images – Remote Images, Text on Images, Pixalation

HTML – URI and URL miscoding

Headers – From Domain and Alias Recognition

Subject Line – Spam Words, Spelling

Body – Spam Words, Spelling

So it all comes down to one point in email deliverability and Spam Filters. As Filters get more sophisticated, it means less emails make it to the inbox, so know what you’re up against.