One of our users just designed a nice email campaign for his client, and tested it in our Inbox Inspector. Overall, he received a passing score, but we noticed something in the spam filter checker.
As you can see, Spam Assassin gave it a full 2.6 points for that! They say the default threshold for Spam Assassin is "5" but we tell people to try to stay below "3" (because c’mon—who really keeps their threshold at 5 these days?). Better safe than sorry.
Our customer really had a nice looking template, and wasn’t trying to hide anything. But spam filters think that tiny fonts are a sign that some spammer is trying to embed a whole bunch of confusing content into their message to throw off their scent.
Our customer’s footer had text specified with: "font-size:9px." Interestingly, our own email templates specify our font size to be 10px, but we’ve never been flagged for that.
So if you have fonts in your footer that are really, really small (like we all tend to do), make sure they’re no smaller than 10px in size.
Learn how you can use MailChimp’s Inbox Inspector to test your email marketing campaigns and transactional emails