There's no sense spending a bunch of time designing, coding, and writing your email newsletters, only to get them trapped in your recipients' junk folders. That's like those salmon you see on TV. They make the long, once-in-a-lifetime journey from the ocean to return to their birthplace and spawn. They fight their way upstream for miles and miles. They make that final jump up the waterfall---then land right in that hungry bear's mouth. D'oh!

If you want your emails to be read, don't do anything "spammy" to get caught by the spam filters. Here are some tips...

How Spam Filters Think

When you send an email campaign to your recipients, your messages have to get past: 1) their ISP spam filters, then 2) their email application spam filters. It's a lot easier than you think for an innocent, legitimate email to be mistaken as spam (this is called a "false-positive"). So it helps to understand how spam filters work, and what they look for. Spam filters analyze the following... (we'll elaborate the chart further down the page.)

What Spam Filters Check: What They're Thinking:
Your Subject Line "Did the sender use "spammy" words and phrases?"
Who the message is addressed "To:" "Did the sender even know the recipient's name, or is it just addressed to an email (which they could have easily guessed, or programmed a script to generate)?"
The content of your message "Is HTML email coded properly? Did the sender take the time to create a plain-text alternative? Does the content contain spammy words or phrases?"
Your IP address "Was the email sent from a server that is on a blackhole-list, or is known to be spam-friendly?"
The sender "Friend, or foe? Is the sender in my address book or contacts list?"
Your "from" email address "Is the email address faked? Is it from a free email account, or does it sound too anonymous?"
Your domain name "Is the sender using a valid domain name that he owns, or is it an anonymous looking, or faked?"
Advice from other spam filters "Has this same message (or sender) already been reported as spam by other recipients, or other spam filters out there?"

Subject Line
The subject line is the easiest way to get your email filtered as spam. Even if your email doesn't get filtered as spam, your subject line is how your recipients judge whether or not to open or delete your message, so it's got to be relevant. Here are some tips for crafting your subject line:

  • Write it so that in the blink of an eye, a recipient knows: 1) who sent it, and 2) what it's about. Also see: "Surviving the Inbox Whack-a-mole Game" at the MailChimp Blog.
  • Make it intriguing, but in a way that's relevant to your audience, and that reinforces who sent the message, and what it's about. For instance, if we sent a MailChimp newsletter with the subject line, "FREE WHITEPAPER INSIDE!" we'd be idiots. Something like, "Whitepaper: Advice for improving your newsletter open rates" would be better.
  • Avoid spammy words and phrases, like FREE, mortgage, insurance, act now, casino, limited time, coupons, click now, open immediately, etc.
  • Don't!!! use !!! too!!! much!!! punctuation!!!!!
  • Avoid expletives (this one's a no-brainer)
  • Don't get creative with numbers/characters in place of letters, like: V1AGRA, SW!VEL, H3LL0, etc.

Who the message is addressed "To:"
You know when you check your mailbox (the old fashioned mailbox, not your email), and you get those direct mail pieces addressed to, "CURRENT RESIDENT" or "HEAD OF HOUSEHOLD"? That's pretty impersonal, right? It's painfully obvious that some computer generated that mail. Well, it's the same with email. Don't just address your email newsletter to "email address." Merge their first and last names into the to: field. Here's how you personalize the To: field with MailChimp.

Content of Message
Spam filters look for "spammy" clues both on the surface, and "under the hood" of your email's content:

  • Don't use "spammy" words and phrases (see above) in your content. It's easier than you think to accidentally use spammy words, like "New XXX-Large T-shirts Available" or "Join us for Casino Night!" or, "Click now to download." Put down your "Copywriting that SELLS!!!!" book when you're writing your email newsletters. Many of the call-to-action "tricks" you might have learned in the direct-marketing world will just get you in trouble with spam filters.
  • Don't just send a giant graphic. That's what spammers do. Your HTML email needs a "healthy balance" of graphics and text. If you're just sending a simple invitation, or a simple promotional piece to your recipients, and all it takes is a simple graphic, you can still include text in the footer area, such as your "unsubscribe" link, your physical mailing address, etc.
  • Always include a plain-text alternative with your HTML email. Spammers are lazy, and don't bother to do that. It may seem like a hassle to write both versions of your email, but you really need to include it. Plus, we generate it for you, so no excuses! And don't skimp on the plain-text version either. In the past, we've gotten a little lazy, and made our plain-text alternatives say, "You're viewing this because you can't view HTML email. Visit this URL to view our message in your browser." Nowadays, spam filters compare your plain-text alternative to your HTML email. If 95% of the message is in HTML, and 5% is in plain-text, that looks sloppy and lazy to the spam filters.
  • Is a domain you're using as a link (like a link shortening service) on a blacklist? Check out this blog entry about what can happen in that case: Is Your Domain Name Getting You Blocked?
  • Check this link we posted on our blog to view the huge list of criteria that Spam Assassin uses to filter email.
  • Most Common Spam Filter Triggers - a recent guide.
  • Code your HTML email properly. If your HTML email is coded sloppily, you'll look like a spammer. Broken images, missing tags, and non web-safe colors are some of the things they look for. Don't use Microsoft Word to generate your code (the code it generates is atrocious). Heck, some spam filters will penalize you for using Microsoft Front Page to code your emails! Learn how to code HTML properly. Or pay someone to do it for you.

IP Address
Some spam filters sync up with "blacklists," which are published directories of spam-server IP addresses. If your email server's IP address is on a blackhole list, the spam filters won't let your email through. The bad news is that you can easily wind up on one of these blackhole lists, even if you're not sending spam. For instance, if a spammer is using a server at your ISP, and his server is within your server's "IP Range," all your emails could get blocked too. That's like the post office blacklisting your "house," because you live in the same "neighborhood" as a known criminal. That seems like a drastic measure, but spam is a drastic problem.

It's particularly a concern for email service providers (like MailChimp). If just one of our users does something stupid, they could get our servers blacklisted, and ruin it for all our users. This is why we're so vigilant about watching all outgoing email from our queue.

What's really scary is that anybody that runs an email server can create his own little blackhole list, and share it with others. It's up to that server admin to determine who gets listed, why they get listed, and if/when it ever gets de-listed. Needless to say, under this scenario, "spite listings" can become a real problem.

The good news is that the major ISPs and email servers out there only sync up with responsible blackhole lists, not just any old blacklist it finds. SpamCop is an excellent example of a "responsible" blackhole list service, because it uses reports from a large network of registered users, and only blacklists servers that have surpassed a certain threshold. Furthermore, if spam reports for a blacklisted server subside, SpamCop proactively de-lists that server.

Sender's Email Address: Friend or foe?
Some spam filters use the concept of, "never take candy from a stranger." If the recipient hasn't "white listed" your email address as a "Friend" or "Buddy," or if your email address isn't in their address book, contacts list, or "sent" folder, you're perceived as a stranger. And if you're a stranger, the spam filter will automatically categorize your email as junk, or it will use much more stringent criteria when judging your email's "spaminess." When people sign up for your email list, it's a good idea to ask them to "please place this email address in your address book, to ensure proper delivery..." Place that request on your subscription confirmation screen, and all welcome emails. Some people place that text at the top of every newsletter they send.

And while we're on the topic of your email address, it's best if you're not using something anonymous, like a free email account (,, etc). While we do allow those as it's not a guarantee of a block, if you have other issues (like with your content or subject line) having a free or public email domain on your reply-to address will ding your spam score even further. For best results - setup a real email address with your company domain name. Get your users to whitelist it. Don't change it.

Domain Name
Some spam filters will check to make sure that an email claiming to be originating from a domain name actually did originate from that domain name. This is called "authentication" and it's slowly becoming more and more common. Emails that aren't "authenticated" are either classified as "junk" or are flagged as "suspicious." To learn more, Yahoo! has published info on its own authentication method (DomainKeys). Microsoft has published details about its Sender Policy Framework, or SPF. You can see how that works in MailChimp here.

Community-based reporting
Many webmail programs and ISPs use community-based reporting to block unwanted email. The concept is pretty neat. Its millions of users get billions of emails every day. Whenever your recipient clicks their "this is junk" button for a particular message they received, that "complaint" is sent to the ISP's server. If enough of its users report an email from you as junk, the ISP will block all your future email to their servers. Here's more information on Gmail's report spam button.

Conclusion: Don't Be Paranoid About Spam Filters

Most of the sophisticated spam filters out there aren't "black or white" with their algorithms. They're usually "realistic" about email, and use a well-rounded combination of the above criteria. SpamAssassin is an excellent, open-source example that you can learn from. It assigns certain "severity points" for each "rule" an incoming message breaks. For instance, using "CLICK HERE!!!" might get 0.5 points (for each occurence in the message), while using bright red fonts might get 0.1 points , and including the word, "V1AGRA" in the subject line might get 4.0 points. It tallies up the total score, and if it exceeds a certain "threshold" (which is set by the person who installed it on the server), the email is categorized as "spam."

When you write your email newsletter, you shouldn't be paranoid about using the phrase, "Click here" once or twice in the email. As long as the rest of your email is in proper order, and you don't violate too many of the rules and criteria we've outlined above, spam filters will let you through.

If you think you may be having a problem with spam filters you can pass your campaign through some real spam filters using our Inbox Inspection tool! We'll give you specific reasons and information on why you're getting filtered.

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