The majority of large internet service providers now use rigorous spam protection mechanisms to trap unsolicited email before it gets into their customers inboxes. Spam filters generally 'rank' each email by a number of different criteria, and, if that email rates above a certain level (such as 10 spam points), then it is flagged as spam and deleted.
Each spam filter functions a bit differently, though, and “passing” scores are typically determined by individual server administrators.
As for that list of spammy criteria, it’s constantly growing and adapting, based on—at least in part—what people identify as spam with the ‘Mark as spam’ or ‘This is junk’ button in their inbox. Spam filters even sync up with each other to share what they’ve learned. There’s no magic formula—and spam filters don’t publish details regarding their filtering practices—but there are steps you can take to avoid landing in your subscribers’ junk folder.
Some spam filters will flag emails based on specific content or images they contain, but there’s not an all-encompassing set of best practices to follow or things you absolutely need to avoid.
- Make sure your emails don't get flagged as spam - and deleted before they even get to your subscribers - avoid using words such as 'Free', '$$$', 'Save', 'Discount', etc in both the subject line and the content of your email.
- Don't use too many images, and not enough readable text. Spam filters can’t read images.
During Mailchimp's user research, they found some surprising spam filter triggers. Here are some examples:
- The phrase, "extra inches" will get you a score of 3.1 by spam assassin. The phrase sounds like it came from some kind of "appendage enhancement" pharma-spam, right? Turns out it popped up 4 times in Mailchimp, from relaxation & beauty spas. As in, "if your new years resolution is to shed some extra inches off your waistline, come in and…"
- Dear FNAME, = "not very dear at all!" Do you merge the recipient’s FNAME into your messages? If so, don’t use the d-word. Turns out "Dear" will get you 2.7 spam points. That’s about halfway to getting your email blocked. Use something else, like "Howdy."
Don’t use purchased, rented, or scraped lists
Not only are they notorious for providing bad addresses that lead to high bounce rates and blacklisting, they don’t actually help you grow your business. Sending to a list that hasn’t given you express permission can impact your ability to market your business, potentially damage your brand, and even result in legal ramifications. Instead, grow your list organically.