I've just gone through a boatload of "pseudo"-spam. Pseudo-spam is what I call legitimate e-mail that, when using a vanilla installation of Spamassassin, is marked as spam solely through the e-mail creator's carelessness, thoughtlessness, whatever adjective you want to use (I refrained from using stupidity although I desperately wanted to). This morning, 25% of the number of e-mails that were classified as spam were actually legitimate. After analyzing the Spamassassin rules that were triggered, many rules were needlessly fired. Had the creator taken the time to format the html properly, many of the rules wouldn't have been triggered.
Just to be clear, I'm talking about all those newsletters that stores like Macy's, Banana Republic, Nordstrom's, etc., and airlines like Southwest and American Airlines and services like Verizon and ATT and your electric company send out that the user signed up for. Big companies. Legitimate e-mail. You signed up for it.
I assume that the main reason a legitimate company sends a marketing e-mail is to get information out to the customers/potential customers. Not running it through a vanilla installation of Spamassassin before you press the send button is shooting yourself in the foot. Not running it through an HTML validator is shooting yourself in the other foot.
1. Less is more - The more html you've got in an e-mail the more chance you have of a mistake. And the more chance you have of it being marked as spam. From a business perspective, so many of the legitimate marketing e-mails are chock full of content. So much so that they distract you rather than focus you on the one or two important points. Streamline your e-mails.
2. Use an html validator if you insist on using html e-mail. I hate looking at garbled stuff.
3. Remove the comments from the html. Make your e-mail's size smaller. Use less bandwidth. Let me use less bandwidth. On a recent e-mail from a popular store, 15% of the content was comments that the html coder had inserted into the file that the user would never see.
4. If you have to put one of those "If you can't see this e-mail click here to view this email in your browser" messages in your e-mail, you probably shouldn't send it out.
As I tweak my Spamassassin configuration, it will be interesting to see what happens with the marketing e-mails.
Also see HTML E-mail.