It’s estimated that a staggering 85% of emails sent globally every day are spam.
That’s over 336 billion unsolicited, unwelcome, and often harmful messages.
To combat this, email service providers have continuously refined sophisticated spam filters to block and prevent spam from cluttering inboxes. These filters analyze an email’s content, sender behavior, and formatting to determine whether it qualifies as spam. While these filters are incredibly efficient, they can sometimes overreach and mislabel legitimate emails as spam.
In this comprehensive guide, we’ll walk you through key strategies and technical insights to keep your emails from being flagged as spam, whether by automated filters or your recipients. From mastering email content to advanced email authentication methods, here’s how you can ensure your emails land in inboxes every time.
Updated Tips for 2025: How to Stay Out of Spam Filters
1. Choose Your Subject Lines Carefully
Certain words and phrases can trigger spam filters, especially if they create urgency, sound too good to be true, or relate to restricted industries. Avoid using these examples:
- Act now
- Free gift
- Buy direct
- Congratulations
- Risk-free
- Limited-time offer!!!
Grammar is equally important:
- Avoid excessive capital letters (e.g., “LIMITED TIME ONLY”).
- Do not overuse punctuation (e.g., “Save BIG NOW!!!”).
- Stay clear of misspellings and questionable phrasing.
Keep your subject lines concise, professional, and relevant. Avoid including domain names, as this can also be a red flag for spam filters.
2. Focus on High-Quality, Relevant Content
The same rules for subject lines apply to your email content:
- Avoid sensational language or exaggerated promises (e.g., “Lose 10kg overnight!”).
- Refrain from using words linked to violence, illegal activities, or spammy industries like “pharmaceutical” or “gambling.”
- Structure your email for easy readability and engagement: short paragraphs, bullet points, and compelling, original content.
Spam filters value consistency and professionalism. Sending personalized emails that genuinely resonate with your audience can also boost deliverability and reduce spam complaints.
3. Simplify Your Email Signature
A cluttered email signature can set off spam filters. Limit:
- Overuse of HTML code
- Excessive links (especially third-party ones)
- Embedded images with hyperlinks
Stick to plain, professional, and minimal signatures that align with your brand identity. Include essential information such as your name, role, and company, along with a contact phone number or website URL—but keep it simple.
4. Balance Text and Images
Overloading emails with large or numerous images can make them seem spammy. To strike the right balance:
- Ensure images make up no more than 50% of your email body content.
- Compress your images to reduce file size (keep it under 200 KB per image).
- Use descriptive “alt” text for accessibility.
A mix of engaging visuals and well-structured text helps build trust and passes spam filter evaluations.
5. Avoid URL Shorteners
Shortened URLs (like bit.ly) are commonly used by spammers to mask harmful links, making them an instant red flag for spam filters.
Instead, use:
- Full URLs displayed as hyperlinks (e.g., “Click here to view our new collection”).
This strategy also reassures recipients by offering transparency about the destination link.
6. Authenticate Your Email With SPF, DKIM, and DMARC
Proper email authentication improves deliverability by demonstrating that your messages are from a verified source. Here are the key authentication methods to implement:
SPF (Sender Policy Framework):
SPF prevents spammers from forging your email address by specifying which mail servers are authorized to send emails on behalf of your domain. To update your SPF record:
- Access your domain’s DNS settings.
- Add or update the SPF record to include all authorized sending services (e.g., “v=spf1 include:mailchimp.com include:mailgun.org ~all”).
- Test your SPF record using tools like MXToolBox to ensure proper configuration.
DKIM (DomainKeys Identified Mail):
DKIM adds a digital signature to your emails, verifying their authenticity and confirming they haven’t been tampered with in transit. Steps to enable DKIM:
- Generate a DKIM key in your email service provider (e.g., Mailchimp, MailerLite).
- Add the DKIM public key as a TXT record in your DNS settings.
- Test your setup to ensure it’s functioning correctly.
DMARC (Domain-based Message Authentication, Reporting & Conformance):
DMARC works alongside SPF and DKIM to protect your domain from unauthorized use. It also provides detailed reports about email delivery. Implementing DMARC involves:
- Adding a DMARC record to your DNS settings.
- Setting policies (e.g., “none” for monitoring, “quarantine” for suspect emails, or “reject” for blocking unauthenticated emails).
- Using DMARC tools to review your domain’s email activity regularly.
By integrating SPF, DKIM, and DMARC, you build trust with email providers and reduce the risk of being flagged as spam.
7. Best Practices for Popular Email Marketing Platforms
Mailchimp:
- Audience Management: Regularly clean your email list to remove inactive or invalid addresses.
- Templates: Use Mailchimp’s built-in templates for optimal formatting and mobile responsiveness.
- Automations: Leverage automation workflows, like welcome sequences or abandoned cart reminders, to engage subscribers effectively.
MailerLite:
- Personalization: Use MailerLite’s merge tags to customize subject lines and email content.
- A/B Testing: Experiment with subject lines, send times, and content to find what resonates best with your audience.
- Segmentation: Group subscribers by interests, demographics, or behaviors to deliver targeted campaigns.
Brevo (formerly Sendinblue):
- Deliverability Optimization: Configure SPF, DKIM, and DMARC settings directly within Brevo for seamless authentication.
- Dynamic Content: Use Brevo’s advanced personalization options to dynamically adjust content for each recipient.
- Detailed Analytics: Monitor open rates, click rates, and bounce rates to refine future campaigns.
Each platform offers unique tools, so familiarize yourself with their capabilities to maximize your email marketing efforts.
8. Monitor Your Sender Reputation
Your sender reputation is a score assigned by email providers, reflecting your trustworthiness. Poor practices like high bounce rates or frequent spam complaints can harm this score.
To maintain a strong sender reputation:
- Send emails only to verified, engaged subscribers.
- Avoid purchased email lists.
- Regularly monitor your reputation using tools like Google Postmaster Tools.
Ensure Your Customers Don’t Mark You as Spam
Even if your emails bypass spam filters, recipients can still mark them as spam. Here’s how to keep them happy:
1. Respect Email Frequency
How often you send emails should align with your industry and customer preferences.
- A bookstore might benefit from weekly newsletters on new arrivals.
- A car service company may only need to email around MOT reminders.
Over-emailing can frustrate recipients and increase your unsubscribe rates. Research shows that nearly 90% of consumers prefer receiving emails once a month.
Tip: Regularly survey your subscribers to learn their preferred frequency and content topics.
2. Implement Double Opt-In
A double opt-in process sends a confirmation email when a new user subscribes to your list, ensuring they’re genuinely interested.
Why it works:
- Prevents accidental or fraudulent sign-ups.
- Improves open rates, engagement, and sender reputation.
Final Thoughts
By following these updated tips for 2025, you can improve your email deliverability, avoid spam filters, and build trust with your audience. Whether you’re using Mailchimp, MailerLite, or Brevo, applying authentication protocols like SPF, DKIM, and DMARC ensures your emails not only reach inboxes but also establish credibility. Coupled with thoughtful audience management and relevant content, these strategies set you up for email marketing success.
