You’ve got enough exciting stuff to worry about. Let us be the reliable platform you can depend on. Make an average $68* for every $1 you spend. So boring.
Take some time to think about this. You’ve worked hard to create the perfect outreach campaign. Your headline is great, the email copy is compelling, and the offers in the email are attractive.
So far, so good.
And yet, your emails end up in your recipient’s spam folder. Unfair, isn’t it?
Well, most email clients have spam filters that protect users from unwelcome emails. While these spam filters do a good job of keeping spammers at bay, they can also send your legitimate sales emails into the junk folder.
This can be painful, especially when you know that your email campaigns are relevant to your recipients.
So, how do you avoid spam filters and ensure your emails are actually delivered to your recipients’ inboxes?
In this post, you’ll learn:
What spam filters are
How email spam filters work
How to avoid email spam filters
Omnisend improves your deliverability and helps your sender reputation
If you don’t have time to read the whole article, here are the key takeaways:
Use reliable email marketing software and authenticate your domain to establish credibility with email providers and improve deliverability rates
Implement double opt-in signup forms and only email users who gave permission — never buy email lists or send unsolicited emails
Write engaging subject lines while avoiding spam trigger words, all caps, and excessive punctuation
Make unsubscribing easy and remove inactive subscribers regularly to maintain list hygiene and a strong sender reputation
Comply with anti-spam laws like CAN-SPAM, CASL, and GDPR by including physical addresses, clear opt-out options, and protecting user data
Want to learn more? Just keep reading.
What is a spam filter?
An email spam filter is a security tool that screens incoming messages to detect and quarantine harmful or unwanted emails. Email providers like Gmail, Yahoo Mail, and Outlook use these filters to protect inboxes from malware, phishing attempts, and unsolicited bulk emails.
Here’s an illustration showing how spam filters work in practice:
Spam filters directly impact your campaign performance and ROI. These filters analyze sender reputation, email content, and user engagement to determine if your emails are legitimate and worthy of subscriber inboxes.
For your marketing campaigns to succeed, your emails must clear these spam filters to reach the inbox where recipients can engage with your content.
Messages caught by spam filters land in junk folders where subscribers may never see them, wasting your marketing efforts and killing potential sales. You should treat every unsuccessful email as a missed opportunity to connect with customers and drive revenue.
How do spam filters work?
While email providers don’t reveal their exact filtering methods, spam filters operate through multiple automated checks that happen in milliseconds when an email arrives:
Technical checks
Analyze the sender’s IP address history and reputation
Look for these essential deliverability features when selecting an email service provider (ESP):
Authentication tools: Built-in SPF, DKIM, and DMARC setup
Reputation management: Strong IP domain reputation
Content optimization: Spam testing and content analysis tools
Compliance support: GDPR and CAN-SPAM-compliant features
Performance monitoring: Detailed deliverability analytics and reporting
Beyond deliverability, your ESP should have a pricing structure that delivers value and provides the marketing features your business needs to thrive. These include:
List building tools
Customizable signup forms with built-in consent mechanisms
Popups and landing page builders with GDPR-compliant opt-in processes
Engagement features
Segmentation based on behavior and preferences
Automated workflows for welcome series, abandoned carts, and post-purchase
Mobile-responsive templates with drag-and-drop editors
Integration capabilities
Seamless connection with your ecommerce platform
API access for custom integrations
Data sync with your CRM and analytics tools
Choose an ESP that balances strong deliverability infrastructure with the marketing features your business needs. Remember: The most sophisticated spam prevention won’t matter if you lack the tools to create engaging, targeted campaigns that drive results.
Omnisend gives you all of its email marketing features on every plan
Some countries and regions have anti-spam laws you need to abide by when sending electronic messages. The laws are meant to protect users from spammers. You must familiarize yourself with them or you’ll pay a hefty fine for non-compliance.
Some of the anti-spam laws you need to comply with include:
CAN-SPAM Act: Senders must give their physical address, not use misleading information, and make it easy for users to opt out
The next tips in this post resemble many of the requirements in these anti-spam laws. Read on to discover how to comply with these laws and boost your email deliverability.
Domain authentication proves you’re a legitimate sender by linking your domain to your ESP’s sending infrastructure. Authentication happens through three key protocols:
SPF (Sender Policy Framework): Verifies emails come from authorized IP addresses
DKIM (DomainKeys Identified Mail): Adds a digital signature to prove emails weren’t tampered with
DMARC (Domain-based Message Authentication): Sets policies for handling authentication failures
Without authentication, you send from generic domains (like sender.platform.com), signaling to spam filters that you might be hiding your identity. Authenticated domains show that you’re a real business investing in proper email practices.
Every ESP has a slightly different authentication process, so check your platform’s documentation for setup steps. The effort pays off through improved deliverability, sender reputation, and brand trust.
Double opt-in is where the visitors who fill out a subscription form are required to confirm their registration in a separate email.
People who go through the trouble of confirming their subscription are less likely to report your email messages as spam as they genuinely meant to subscribe to your emails.
The animation below shows how double opt-in works to avoid spam filters. The visitor first provides their email address to subscribe to the company’s newsletter, and then they get an email asking them to confirm their subscription:
Here’s what the email confirmation looks like:
Omnisend makes it easy to add double opt-in to your emails. Just go to Behavior settings > Audience management > Enable double opt-in, then customize your emails and landing pages.
Your sending behavior plays a huge role in email deliverability and avoiding spam filters. Sending an email campaign to a large number of recipients from a newly created IP address is considered risky behavior and comes across as an instant red flag for email clients.
As such, email providers may hesitate to deliver your emails to your recipients’ inboxes, opting instead to send them to the junk folder.
To prevent this from happening, you should warm up your IP address by keeping the email volume low at first and gradually increasing the quantity over time.
Additionally, send no more than one campaign per day, three times a week.
Increasing your sending volume gradually will help you build your IP’s reputation. It will help email providers understand your sending behavior, list accuracy, and user response.
If everything is positive, then email providers will have no reason to send your emails to spam.
Watch this video to find out more about optimizing send times:
Nothing will see your email campaigns labeled as spam faster than sending them to users without their permission.
So, instead of wasting your resources buying an email list, concentrate your efforts on growing your subscriber list organically.
Lists that have been built organically have higher open rates and fewer spam complaints than those that have been bought or scraped. High open rates and fewer spam complaints are the signals you need to convince email providers that your emails are meant for the inbox.
Rather than sending similar emails to everyone on your list, segment your email list and send targeted emails to specific groups to avoid spam filters.
Doing so ensures your recipients receive emails that are relevant to them. This will increase your email open rates and reduce the number of deleted emails. This signals to email providers that your emails are valuable to your users — hence, they should be delivered to their inboxes.
While subject lines affect your open rates, they also play a role in whether your emails will be flagged as spam. Someone can quickly look at your email subject line and decide to mark the email as spam without even opening it.
That’s why you need to take extra care with your subject lines so you don’t end up creating a negative impression with your email subscribers. Here’s what you need to do to create impactful email subject lines:
Don’t use all caps in the subject line
Avoid exclamation marks
Avoid over-using spam trigger words like “free,” “now,” and “guarantee”
Personalize the subject line to the recipient
Make the subject line as descriptive as possible
Not sure if your subject lines pass the spam test? Check your subject lines in seconds with our free email subject line tester.
9. Lose words that trigger spam filters
When writing your email copy, you want to limit the use of spammy words that can make readers flag your emails as spam.
If a word sounds desperate, it shouldn’t be used in your emails. You also want to avoid words that are pushy and those that sound too good to be true.
Below is a table of spam-triggering words you need to avoid:
Make money
100% free
Cash bonus
Get extra cash
0% risk-free
Instant bonus
Save big
Win $$
Don’t miss this
10. Don’t add attachments
Email attachments can trigger spam filters and create slow-loading emails that frustrate subscribers so much that they add you to their spam folder. Instead:
Compress and host essential files on cloud services (Google Drive, Dropbox) and share secure links
Embed small images directly in the email body with a “View More” CTA to your website
Use GIFs instead of video files, linking to the full video
For tickets or documents, use specialized platforms (Eventbrite, DocuSign) and include access links
Consider file size limits — keep embedded images under 1MB
The goal is to create lightweight emails that load fast and don’t raise red flags with spam filters.
11. Welcome new subscribers
Welcome emails are a wonderful opportunity to make a good first impression with your subscribers. Done well, your subscribers will look forward to your emails and open them when they land in their inboxes — a fantastic way to avoid spam filters.
You can also ask new subscribers to add you to their safe sender list to ensure that your emails don’t go into spam for them. Another worthwhile idea is welcoming subscribers with a discount, free shipping, or other incentive to encourage email engagement.
Email engagement directly impacts deliverability. When subscribers consistently open and click emails, spam filters learn to trust your sending patterns. Poor engagement, such as instant deletions or low open rates, can harm your sender reputation.
Make every email count with these steps:
Use high-quality imagery that captures your market
Write compelling subject lines that match your content
Personalize based on subscriber behavior and preferences
Structure content for easy scanning with clear headings and short paragraphs
Focus each email on a single, clear purpose
Test different content types to see what drives engagement
Keep mobile readers in mind — use plenty of white space
The more value you provide, the more subscribers will engage, and the better your deliverability. Quality content builds both customer relationships and spam filter trust.
Skincare brand Hello Bubble has its emails down to a fine art form, using fun images and clear CTAs to encourage engagement during Black Friday:
Access your email list periodically to identify inactive subscribers and remove them from your list to avoid spam filters. Inactive subscribers harm your delivery rates, and this could see your emails labeled as spam. Poor deliverability also comes across as a negative sign to email clients.
That’s why it’s important to perform a regular email list analysis to determine your active and inactive subscribers.
Do the following to keep your email list clean:
Segment your subscribers into active and inactive users
Add subscribers that lapsed not more than two months ago to a reactivation campaign
If the lapsed subscribers don’t engage, remove them from your email list completely
Prefer a video to learn how to keep your email list clean? Here you go:
15. Maintain a strong sender reputation
Your sender reputation determines if your emails reach inboxes. Email providers score your domain based on sending patterns and recipient behavior:
Sending patterns: Consistent, predictable sending volumes to build trust
Bounce rates: Keep below 2% by regularly cleaning your list
Engagement metrics: High opens and clicks boost your score
Spam complaints: Keep under 0.1% with relevant content and clear unsubscribes
Spam traps: Regular list cleaning prevents hitting these reputation killers
Unsubscribe rates: High rates signal irrelevant content — aim for under 0.5%
Check your reputation score using tools like Talos Intelligence or Sender Score. Monitor these metrics monthly and address issues quickly to maintain strong deliverability.
Provided your email campaigns are relevant to your users and you follow the guidelines we have mentioned above, you’ll greatly enhance your chances of avoiding spam filters.
Ultimately, the best email deliverability rate comes down to using reliable email marketing software that allows you to create appealing email campaigns and send them from a reliable server.
Reach more subscribers with Omnisend’s built-in spam tools
Bernard is the Sr. Director of Communications & Creative at Omnisend, with a passion for good research, helping ecommerce businesses with their marketing automation needs, and beating absolutely everyone in Mario Kart 64.
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