As you begin email marketing campaigns, it's inevitable that you'll eventually run into issues with spam filters preventing your emails from being delivered. Industry statistics show that about 20% of all email marketing campaign emails end up getting lost to spam filters. Even with permission-based subscriber lists, legitimate emails can still get lost in the fray and get earmarked for deletion. Learning how spam filters work will help you better craft your emails to increase open and engagement rates.

Defining Spam

Spam is defined as any unwanted email messages that are considered irrelevant to their recipient. They're not limited to just advertisements. Nonsensical emails sent to personal email addresses or solicitations to businesses for upcoming events or programs are also considered spam. Modern email inboxes feature the ability to mark emails as spam to prevent the sender from sending similar emails to you and similar email users in the future. Unless you give permission to an email sender to send you unsolicited mail, it's broadly considered to be spam.

Legality of Spam

Fortunately for Internet users, spam is considered illegal in the United States. In 2004, the US Congress passed a law called the "CAN-SPAM Act of 2003" that made it illegal for businesses to send unwanted email to individuals or businesses who didn't ask to receive the promotional materials. If emails make their way into an unsubscribed recipient's inbox, they're legally entitled to be able to unsubscribe themselves from future mailings.

Violations of this law can fetch penalties of as much as $11,000 per email address emailed without permission. Avoiding these penalties can be achieved by not using deceptive names or subject lines to try and bypass spam filters built into inboxes. Attempting to bypass these anti-spam filters is considered a violation of the law and could lead to hefty fines. Similar anti-spam laws are also seen in other countries around the world.

Understanding Spam Filters

Although spam filters are widely considered effective at doing their job, many marketers are still unfamiliar with how the filters decide which emails to throw out and which ones are legitimate.

Filters first work to judge the overall quality of an email, scanning for phrases that indicate a business offer is included. Discounts that include percentages like "10% off," or common phrases like "free sample" are the first to get detected. Following that, common phrases used to indicate urgency are also ignored.

Generally speaking, spam filters work by assigning "point" values to each of the offenses they find in an email. Emails that score too high on the filter's scale, meaning they included too many spammy qualities, will be delivered to the spam folder and won't make it to the inbox.

Each email server has its own criteria for determining which emails are spam and which ones can go ignored, so while an email may successfully make it into 80% of inboxes in a campaign, the remaining 15-20% of recipients won't know that you reached out.

Basic Things to Avoid

Primarily, you should avoid sending emails with excessive capital letters or punctuation like exclamation points. These basic techniques, usually used to signify a promotional offer, are red flags for spam filters.

Next, avoid using colored fonts in your emails. While basic HTML and newsletter formatting is fine, plain-text emails that try to include colored text around "exclusive" offers are also signals to spam filters to prevent delivery.

Finally, try to provide only quality content in your emails. Emails sent as embedded images with little to no text or emails with unruly HTML will be the first to go to the spam folder. While email servers can't read images (yet), they're savvy enough to know that the majority of emails that avoid using text and only use images are probably the work of spammers.

When it Works, it Keeps Working

One of the biggest factors in determining whether future emails will continue to be delivered is the success of past campaigns. Open rates and engagement rates with previous emails you've sent to your email list will help determine how your future emails are delivered. If a large portion of your subscriber base reported your last email as spam, there's a good chance that your next emails will end up marked as spam by default. If you had low engagement rates previously and you continue to include links in your future emails, spam filters will take this as a sign that your links are not worth clicking on.

Were My Emails Filtered?

An easy way to tell if your latest email blast was successful is to compare the open-rates and engagement rates of your new campaign to those of your previous efforts. If you see sudden drops in engagement or open rates, something about your latest email probably triggered spam filters to prevent it from being delivered to everyone in your list.

Trusted Email Senders

The more emails you send, the more "clout" you build up with anti-spam technology. Because spam filters are able to communicate with each other and share their findings about good and bad email senders, as you develop a reputation for quality emails, spam filters will share that information with each other to slowly increase your deliverability rate to new inboxes.

As a business, it's important to only send quality, business-related emails to your email subscriber list and follow all CAN-SPAM law requirements to prevent hefty fines. Although the occasional email may go undelivered, not abusing your subscription base with promotional offers and advertisements is the only guaranteed way to increase delivery rates.