What are the best practices for email deliverability and avoiding spam filters?
Michael Ko
Co-founder & CEO, Suped
Published 18 Apr 2025
Updated 15 Aug 2025
7 min read
Getting your emails consistently into the inbox rather than the spam folder can feel like a constant battle. It's not just about hitting 'send', it's about navigating a complex landscape of technical configurations, sender reputation, and recipient engagement. I've seen many businesses struggle with this, losing potential sales and important communications because their emails never reach their intended audience.
There's no single magic bullet for perfect deliverability. Instead, it's a combination of adhering to best practices across several key areas. From setting up proper authentication to maintaining a clean email list and crafting engaging content, every step plays a crucial role in improving your inbox placement rates and avoiding spam filters. Let's explore the essential strategies that can make a real difference for your email program.
Technical foundations and authentication
Email authentication is the bedrock of good deliverability. Internet service providers (ISPs) rely heavily on these protocols to verify that an email truly came from the domain it claims to be from, which helps prevent spoofing and phishing. Without proper authentication, your emails are much more likely to be flagged as suspicious and land in the spam folder (or be rejected entirely).
I always emphasize the importance of implementing SPF, DKIM, and DMARC. These three standards work together to build trust with receiving mail servers. SPF (Sender Policy Framework) specifies which mail servers are authorized to send email on behalf of your domain. DKIM (DomainKeys Identified Mail) provides a way to cryptographically sign your emails, ensuring that the content hasn't been tampered with in transit. DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds on SPF and DKIM, telling receiving servers what to do if an email fails authentication and provides valuable DMARC reports that give you insight into your email traffic.
Beyond basic setup, it's critical to regularly review your DMARC record and policy to ensure they are correctly configured and achieving alignment. Misconfigurations can lead to legitimate emails being blocked or marked as spam. For example, a common issue is the SPF DNS lookup limit, which can cause emails to fail authentication if too many authorized sending sources are listed. This is especially true for large organizations or those using multiple third-party sending services.
Authentication protocols
Implementing SPF, DKIM, and DMARC properly is foundational. Use our free DMARC record generator to start or correct your records. These help verify your sending domain and prevent unauthorized use. Failing to configure these can severely impact your ability to reach the inbox.
IP and domain reputation
Your sending IP and domain reputation are paramount. Sending too many emails to inactive or invalid addresses, or receiving a high volume of spam complaints, can quickly tank your reputation. This is where blocklist monitoring becomes essential.
Content, engagement, and list hygiene
Beyond the technical configurations, the content of your emails and how your recipients interact with them are huge factors. ISPs (Internet Service Providers) like HubSpot use engagement metrics, such as opens, clicks, replies, and even whether an email is moved to a specific folder, to gauge sender reputation. High engagement signals to ISPs that your emails are valued, leading to better inbox placement. Conversely, low engagement or a high number of spam complaints can quickly lead to emails landing in the junk folder or being blocked entirely.
Focus on sending relevant and valuable content to an audience who genuinely wants to receive it. This means avoiding spammy subject lines and body text, and providing clear calls to action. Personalization, segmentation, and A/B testing can help you understand what resonates most with your audience, leading to higher engagement. Always ensure your emails provide clear value, whether it's information, discounts, or updates.
Another crucial aspect is list hygiene and management. Sending to outdated or invalid email addresses can lead to hard bounces, which negatively impact your sender reputation. Regularly cleaning your list and removing inactive subscribers or invalid addresses can significantly improve your deliverability. Implementing a double opt-in process is also a highly recommended best practice, as it ensures that subscribers genuinely want to receive your emails, reducing the likelihood of spam complaints and spam traps. Content Marketing Institute emphasizes double opt-in for this very reason.
Engagement monitoring: Keep a close eye on your open rates, click-through rates, and complaint rates. Tools like Google Postmaster Tools can provide valuable insights into your domain's reputation with major ISPs.
Content quality: Avoid excessive use of spam trigger words, overly promotional language, or deceptive subject lines. Focus on clear, concise, and valuable messaging.
List segmentation: Segment your audience to send targeted content. This increases relevance and engagement, reducing the likelihood of recipients marking your emails as spam.
Unsubscribe process: Make it easy for subscribers to opt-out. A clear and prominent unsubscribe link can prevent spam complaints from frustrated recipients.
Regularly testing your email deliverability is a proactive step that can save you a lot of headaches. This involves sending test emails to various mailbox providers and checking where they land (inbox, spam, or blocked). This helps you identify potential issues before they impact your main campaigns.
I often advise using a free email testing tool to get an instant deliverability score and pinpoint areas for improvement, such as issues with your SPF record or content that might trigger spam filters. Remember, deliverability is not a one-time setup, but an ongoing process of monitoring and optimization.
Proactive monitoring
Implement continuous monitoring of your IP and domain reputation. This includes watching for blocklist (blacklist) listings and responding swiftly to any issues. Use tools that provide real-time alerts.
Sender reputation and technical best practices
Warming up a new IP address or domain is a critical, yet often overlooked, practice. If you suddenly start sending large volumes of email from a brand new sender, ISPs will see this as suspicious behavior and are likely to block your emails. A slow, gradual increase in sending volume helps establish a positive sending history and builds trust with mailbox providers.
Maintaining consistency in your sending volume and frequency also contributes to a stable sender reputation. Erratic sending patterns can trigger spam filters. Aim for a predictable schedule, whether daily, weekly, or monthly, that aligns with your subscribers' expectations.
When it comes to the technical side, ensuring your email sending infrastructure is robust and compliant with industry standards is vital. This includes proper DNS records, secure SMTP configurations, and reliable email service providers (ESPs). A reputable ESP will have built-in mechanisms to help manage IP reputation and ensure compliance, although the ultimate responsibility for good sending practices lies with you.
The ongoing journey of deliverability
Building and maintaining good email deliverability takes consistent effort and attention to detail. It's an ongoing commitment to best practices, from technical setup and list management to content quality and recipient engagement. By focusing on these areas, you can significantly improve your chances of landing in the inbox and ensuring your messages are seen by their intended audience.
Remember, the goal is not just to bypass spam filters, but to build a positive relationship with both mailbox providers and your subscribers. This leads to higher engagement, better reputation, and ultimately, more successful email campaigns. Continue to monitor your metrics, adapt your strategies, and stay informed about changes in the email landscape.
Views from the trenches
Best practices
Always use a double opt-in process for new subscribers to confirm their intent and reduce spam complaints.
Regularly clean your email list by removing inactive subscribers and hard bounces to improve sender reputation.
Segment your audience and personalize content to increase relevance and improve engagement rates.
Implement strong email authentication (SPF, DKIM, DMARC) to verify your sending domain's legitimacy.
Monitor your domain and IP reputation regularly using tools like Google Postmaster Tools.
Common pitfalls
Sending emails to purchased or rented lists, which often contain spam traps and invalid addresses.
Not warming up a new IP address or domain gradually before sending large volumes of emails.
Ignoring email authentication protocols, leading to emails being flagged as suspicious or rejected.
Using generic or misleading subject lines and overly promotional content that triggers spam filters.
Failing to monitor deliverability metrics and sender reputation, missing issues until they become critical.
Expert tips
Focus on the quality of your list over quantity, as engaged subscribers are key to good deliverability.
Understand that deliverability is an ongoing process, not a one-time fix; continuous monitoring is crucial.
Don't rely on users marking emails as 'not spam' to fix a bad reputation; organic engagement is more effective.
User behavior significantly impacts spam algorithms; a high rate of positive interactions is vital.
Ensure your email sending infrastructure is technically sound and compliant with current standards.
Expert view
Expert from Email Geeks says there is no single magic bullet for deliverability, emphasizing that it requires a holistic approach.
2020-02-07 - Email Geeks
Marketer view
Marketer from Email Geeks says that avoiding spammer-like behavior is a key factor in having fewer deliverability issues.
