How To Avoid Email Spam Filters | Subject Lines, Trigger Words (2023)

When you press “send” on an email, you can’t just assume it will reach an inbox. One out of four American business emails was marked as email spam or went missing in 2015.

That’s an 11% drop in email deliverability from 2014. Email spam filters are tightening their scope and people are losing tolerance for unsolicited emails.

What this means for you:

When you’re writing emails and compiling lists, 25% of your effort is going to waste.

To help you rise above the average sender’s open rates, here are10 reasons why emails get marked as spam, and how to fix each. Take notes.

Email tracking in your inboxFind out if your emails are making it to the other side

Why Automatic Email Spam Filtering Happens

#1: Your Subject Line Includes a Spam Trigger Word

Sometimes the words you choose are what’s keeping you from reaching your prospect.

This applies most to your email subject line. Words like “free,” “money,” “help” and “reminder” all trigger content-based email spam filters. Especially if you’re not added as a contact in your recipient’s email database.

Here’s a more complete list of email spam trigger words:

Want even more? Here’s a list of 200 common spam words.

The takeaway:Keep this list by you as you type your emails to avoid using these words. You can bookmark this web page or print it out for your desk.

(Video) How to avoid email SPAM filters || 4 tips for E-commerce email marketing | Spam trigger words

If there’s a word that you need to use, keep it out of your subject line.

#2: Your Email Has All Caps


We didn’t think so. Using all caps in an email is game-over just the same.

This one’s that simple.

#3: Your Email Has Exclamation Points

How excited are you about avoiding email spam filters?!?!?!

Like emails with all caps, emails with exclamation points are food for spam catchers. Especially when they’re in the subject line.

Because messages with exclamation points resemble true spam emails looking to scam recipients, they are treated the same by email providers. They’re filtered from inboxes.

It’s the similarity principle. In this case, people have set systems to group emails based on similarities that they have.

Here’s how an email that’s fallen victim to a spam filter shows up in the dark depths of a recipient’s spam folder:

The takeaway: No exclamation points in your subject lines. When you have a minute, also take a look through your own “Spam” folder for patterns to avoid in your own emails.

#4: You’re Using Attachments

Sending an email with an attachment to someone who’s expecting to hear from you (i.e. someone who has you in their Contacts) is okay to do. I’m sure you’ve done it plenty of times without a hitch.


It’s sending an email with an attachment to a new, cold contact that causes an issue. Remember the similarity principle above? Same applies here.

True spam emails often contain destructive attachments, so spam filters supervise (and remove) emails with attachments.

The takeaway: When you’re writing a cold email and you’d like to include a case study or piece of sales collateral, do so with a link rather than an attached doc.

The benefit: you can track the link to see if they open it. And if it’s a multiple-page PDF, tools like Yesware allow you to actually track how long your recipient spends on each page.

And now (drumroll…) I am going to show you examples of all four above spam triggers in action, wrapped into a small snapshot of my “Spam” folder:

#5: Your Email Image to Text Ratio Is High

Messages that are overly graphic will not reach your recipient. Salesforce says so. Your email needs to be more than just an image or many images with little text.

Note: The common rule of thumb used to be to maintain a 60/40 text-to-image ratio. But recent research from Email on Acid shows that restrictions like this depend on the length of an email.

Their findings:

  • Emails less than 500 characters should contain a supporting image

  • Emails over 500 characters are not significantly impacted by image/text ratio restrictions

To give you an idea of what a 500-character email would look like, this message is exactly 500 characters (with spaces).

Emails of this length are typically 5 to 7 sentences long. They give you enough room to introduce yourself in the email, describe why you’re reaching out plus what value you offer, and then request something. Just like that.

(Video) SPAMMY words to Avoid in Your Cold Emails in 2021 | Avoid SPAM Filters

Because sales emails today are kept short in order to draw a prospect’s attention, keep it, and quickly drive action, they often fall within this 500-character range.

The takeaway: Emails with a graphic and no text just about guarantee your email will never see the light of day on the other side. If your email is at or under 500 characters, A/B test it. Use a bulk email tool to split up your recipient list into two. Send the first batch a version with an image, and the second a version without an image. Track campaign performance to see if you have higher opens with one versus another. (Most email platforms don’t measure email spam rates, so you have to infer spam rates from open rates.)

You can also try a free tool like mail-tester to audit your email before sending.

#6: Your Email Has Different Colored Fonts and/or Styles

Live life colorfully, but not in your outreach emails to cold contacts.

Here’s an example of an email that’s definitely spam-bound.

Email spam filters look for variations of colors and font styles as a first flag for removal.

The takeaway: Keep it simple. For each email you send, use no more than 3 font styles/colors total. Don’t forget: hyperlinking a page on your website and bolding your ask gets you up to two.

#7: Low Open Rates

Webmail providers like Gmail are increasingly using recipient engagement to classify an email as spam or not. It’s called “Engagement-Based Spam Filtering.” They identify when a user deletes unopened emails from senders, and begin to filter out these emails from reaching the inbox in the first place.

The takeaway: If you’re sending emails to someone over and over without any opens, then stop. It’s a wasted effort. Use an email tracking tool (Yesware offers a free trial) to see whether emails sent from your company account are getting opened.

“When you find yourself spinning your wheels on an ice cold prospect, use your judgement about when to cut your losses,” says Joel Felcher. “We coach our team to break it off after 5 or six unopened emails.”

Tip: Send your emails at the right time by checking out this free tool [Bookmark for later].

(Video) Email Spam Trigger Words & Phrases To Avoid | Emails Marked As Spam | Avoid Spam Filters| Email Spam

Boost open ratesAlways know what is/isn't working with real-time engagement insights

Why Your Recipient Is Marking You as Email Spam

#8: Your Email Is Unsolicited (and Aggressive)

According to MailChimp, 43% of users report emails as spam if they don’t recognize the From Name or email address. So if they don’t know you, they flag you.

That’s a tough outlook for emailing cold prospects. And once you’re marked as spam, you’re blocked from reaching that person again.

The takeaway:Personalize your email. This tip is becoming a mantra in our blog posts.

Emails with customized messaging for individual recipients see higher open rates (and reply rates). So not only are you NOT being marked as email spam, but your message is considered and answered.

#9: Overeager Follow-ups

Even if your personalized email arrives to an inbox and receives engagement, you can ruin your chances with a barrage of follow-ups.

People respect persistence, but being overly persistent is disrespectful. You need to let your prospect breathe.

The takeaway:If you’re automating your follow-up with a drip campaign, then space out your follow-up emails at least a few days at a time.

#10: Your Subject Line Is Deceptive

Subject lines that spark curiosity get emails opened, but that’s just half the story. Subject lines that misrepresent emails irritate prospects and drive them to flag you as spam.

For example, some sales reps add “Re:” or “Fw:” to guise their cold emails as conversations and pique their prospect’s interest. In reality, this is misleading. And why would a prospect trust you if your first touch with them is misleading? (They won’t.)

The takeaway:Keep your subject line honest (and free from trigger words, all caps, and exclamation points as mentioned earlier).

Want to try different subject lines? Save email templates, get reporting.


How do I stop spam filter subject line? ›

One of the easiest ways to avoid spam filters is by carefully choosing the words you use in your email's subject line. Trigger words are known to cause problems and increase the chances of your email getting caught in a spam trap.

What words should you not use in an email subject line? ›

Learn the 45 words & phrases you should avoid in Email Subject Lines
Act now!All naturalAttention
CertifiedDear friendDiscount
Double your incomeEliminate debtFast cash
FeesFinancial freedomGuarantee
HotIncreaseLose weight
6 more rows

Why is spam in my subject line? ›

The display of [SPAM] in the subject lines of some campaigns is being added by the receiving server's spam filter. Typically this occurs due to something the receiving server did not like about the campaign. The IT team at the receiving domain should be able to explain why it's being considered SPAM.

What triggers Gmail spam filter? ›

Gmail employs a number of AI-driven filters that determine what gets marked as spam. These filters look at a variety of signals, including characteristics of the IP address, domains/subdomains, whether bulk senders are authenticated, and user input.

Do email attachments trigger spam filters? ›

You Included Attachments in Your Emails

While it is common practice to include attachments in emails to people who are expecting to hear from you, doing so in bulk will trigger spam filters. This is because actual spam emails typically contain harmful attachments.

Do links in emails trigger spam filters? ›

Constant Contact emails are enabled with link tracking for your click reports, which changes them slightly. It's best to avoid using the URL as the link text because it will never match the URL behind it and has a high likelihood of triggering a spam filter.

Which of the following words should be avoided on subject lines for better open rates? ›

On the other hand, there are number of keywords that can be detrimental to open and engagement rates, including: Free: Near the top of the list of words to avoid for email subject lines is “free” due to overuse. It can also harm a sender's reputation. $$$: Symbols and emojis are usually triggers for SPAM filters.

Can I use the word free in an email subject line? ›

These examples show that, contrary to popular belief, email providers are delivering emails that contain the word 'free' in the subject line. So yes, you can use it, but it's important to use it in the right context. Your subject line must appeal to your subscribers, otherwise they won't open!

Do exclamation points trigger spam filters? ›

Research shows that exclamation points in subject lines lead to lower than average open rates because this type of punctuation is actually a trigger for spam filters,” the ebook says.

How can the email subject line show below backfire? ›

The goal of your subject line should be to entice high-value prospects to open, read, and act on your email. Email opens are a great first step, but they have no value on their own. In fact, a gimmicky subject line that's focused only on opens can backfire by causing your prospect to react negatively to your message.

What is the subject line of email etiquette? ›

Include a clear subject line

Title your email in a way that the recipient immediately knows what the message is about. For example, if you're emailing to follow up on a presentation, you might write, “Quick question about your presentation.”

How do I stop Constant Contact emails going to spam? ›

If you are a Constant Contact customer, every email you send includes an unsubscribe link. Also, make sure to monitor the inbox for the address you're using to send your email campaigns, as many people will reply to your email and ask to be taken off your list. If they ask, you'll want to promplty remove them.

Do emails without subject go to spam? ›

No Subject = Spammer. For the most part, I do not open emails where the Subject field is blank unless I immediately recognize the sender. This is because most non-subjected emails are spam. Not having a Subject makes you look spammy and generally will have your email end up in my junk folder misidentified as spam.

Can I use the word free in an email subject line? ›

These examples show that, contrary to popular belief, email providers are delivering emails that contain the word 'free' in the subject line. So yes, you can use it, but it's important to use it in the right context. Your subject line must appeal to your subscribers, otherwise they won't open!

What is a good subject line for an introduction email? ›

Address your subject line to a person's name

Be personal in your subject line by using the recipient's first name. This shows the reader that you're sending a personalized note and that you're not just sending out mass emails. Recipients are more likely to open an email if they think it comes from someone they know.


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