In this article, you’ll learn what are spam filters? How and why should you avoid them? And how can you keep your email contact list up-to-date and relevant?

As a marketer, getting customers to subscribe to your mailing list can be the beginning of a beautiful friendship. But, just like any relationship, it takes work.

Think about it: What if someone you don’t know shows up at your door and says, “Hey, do you want to be friends? I bought a pizza.” Even if you really like pizza you’d probably say, “Thanks but no thanks,” and lock the door.

“People who are new to e-mail marketing often don’t realize that not every sent e-mail reaches their recipients.”

The same goes for users. If you indiscriminately send unsolicited emails with suspicious subject lines or messaging to large groups of people, AKA spam, their email servers will block you with their spam filters.

However, even if you’re legit and only send marketing emails to users on your contact list, your emails might be blocked if the content seems generic or overused. Think of it like inbox intuition.

Imagine XYZ’s Watches sends out an e-blast with the subject line, “Our incredible sale is now on!!!” to their customers, announcing their holiday sale. Although they are a popular and legitimate brand, the email ends up in users’ spam folders.

Spam filters don’t just block unwanted emails. They can also learn to detect different types of spam.

They do this by analyzing the email’s content, subject lines, metadata, IP address, code, and format — among other things. For example, some spam filters can tell if the email’s body text was dragged-and-dropped from a word processing program.

Also, it doesn’t matter if users would be interested in the content of the email. If they didn’t give you explicit permission to send them messages, it may be considered spam.

Spam filters are set up so people won’t be bombarded with annoying or inappropriate messages, and to protect them from scammers. (Spoiler alert: That Nigerian prince isn’t real.)

They also exist so legitimate businesses that don’t spam aren’t drowned out by imposters. However, this means that sometimes, despite your best intentions, your emails can get mistaken for spam.

So why don’t spam filters tell marketers exactly what to avoid? Because if they did, they’d be unintentionally giving that information to spammers, too. However, there are things you can do to help your emails end up in the inbox.

The first step to making a connection is to get personal. If your email begins with “Dear valued customer,” it’ll trip the alarm.

Think about how it feels to get a text from a friend versus an unknown number. Well, spam filters can detect if you have friendly information like first or last names, and might flag emails if you don’t include it.

Interesting Fact: According to Steve Ballmer, Microsoft founder Bill Gates receives four million emails per year, most of them spam.

Give users options as to what kinds of emails they want to receive. For instance, if you distribute a newsletter and lots of event invitations, ask users if they want to subscribe to both, or just one.

Use a “double opt-in” system: After a user has opted in, show them an exit screen that tells them you’ve sent them a confirmation email. In the email itself, ask the user to click a link to approve and finalize the opt-in.

Make the unsubscribe button or link easy to find in the email footer. Users might want a break from receiving your emails, so it’s better to have them unsubscribe than to flag them. This helps keep communication channels open for the future.

Even if users give you their email addresses as part of a purchase, you can’t send a marketing campaign message to those addresses because it will get flagged. Instead, send out an initial email from your personal account telling them about the campaign, and allowing them to opt in.

Spam filters analyze everything from content to formatting. Make sure your emails look professional and match your brand’s style and identity.

After acquiring an email address, don’t wait too long before starting communication. Send out an email right after the user has opted in, giving a sense of the types of content they should be expecting, like deals, news, and more.

Be consistent with your emails, and set expectations about their frequency and content. If you say you’ll send a weekly email, sending one every day isn’t cool.

Avoid using cliché subject lines, like “Click Here!” or “HURRY NOW!!!” On that note, don’t write in ALL CAPS and avoid overusing exclamation points.

You can use HTML to make your emails stand out, but avoid creating emails that have big images, with little or no text. Spam filters don’t read images, so they’ll just assume you’re an overachieving spammer.

Tip: Avoid using purchased lists of leads and emails. These types of contact lists get passed around a lot, and most spam filters know how to detect them.

A true relationship is one that grows over time, so making a connection is only the first step — the next is maintaining and sustaining the relationship.

Internet service providers (ISP) can detect email inactivity. If your emails go unopened for too long, the ISP will label all emails from the forwarding address as spam.

If you notice inactivity from a user, reach out with a personalized message. Instead of sending them the next newsletter, send an email saying “Hey, haven’t heard from you in a while. Just checking to see if you still want to get our emails.”

Also, if a user doesn’t engage with your emails within 6 months, their contact details go to what’s called a “stale list.” In that case, you’ll need to send them a reconfirmation email, and ask them to opt in again.

Another way to avoid having your emails flagged is by monitoring and optimizing them.

If you’re running an email marketing campaign, consider hiring an email marketing expert or consultant to give you stats and reports on the effectiveness of your emails.

In the report’s overview page you can see complaints, AKA “abuse reports,” and check email open rates. Industry standards say that you should aim for a 20-30% open rate, so if yours is lower, you should consider a change.

Check your “hard bounces” and SMTP (Simple Mail Transfer Protocol) replies. Hard bounces happen when the server hosting the email has blocked you entirely. SMTP replies indicate errors, which may include spam filter issues.

It’s hard to get back into the inbox once your domain has been labeled as spam. That’s why you should test your emails before you send them to actual users.

Set up test accounts with free email providers, like Gmail or Yahoo. If your emails aren’t going through, try making some changes before resending. For example, remove a link or change the “from” address.

Avoid using the word “test” in the subject headline. Also, don’t send the email to multiple people within the same company because it will be blocked by the company’s firewall.

If you have a larger budget for email marketing, you can hire an email marketing service, to do testing and monitoring for you.