How to improve email deliverability and reduce spam complaints for newsletters?
Matthew Whittaker
Co-founder & CTO, Suped
Published 31 Jul 2025
Updated 18 Aug 2025
7 min read
Getting your newsletters into the inbox and keeping spam complaints at bay is a constant challenge for email senders. It's not just about hitting send, it's about building and maintaining a healthy relationship with mailbox providers and, most importantly, your subscribers. A high spam complaint rate can severely damage your sender reputation, leading to lower deliverability across all your email campaigns.
Many factors influence whether your newsletter lands in the inbox or the spam folder. From technical configurations like email authentication to the quality of your subscriber list and the content of your emails, every element plays a crucial role. Ignoring these factors can lead to emails being blocked or filtered, making all your hard work go to waste.
In this guide, I will share practical strategies to help you navigate the complexities of email deliverability and significantly reduce those frustrating spam complaints. We'll cover everything from technical setups to content best practices, ensuring your valuable newsletters reach their intended audience.
Email authentication and infrastructure
Email authentication is the bedrock of good deliverability. It tells mailbox providers that your emails are legitimate and haven't been tampered with. Without proper authentication, your newsletters are far more likely to be flagged as suspicious or spam, regardless of your content or list quality. Implement SPF, DKIM, and DMARC to build trust with internet service providers (ISPs).
SPF (Sender Policy Framework) lets receiving mail servers verify that your domain's sending IP addresses are authorized. DKIM (DomainKeys Identified Mail) adds a digital signature to your emails, allowing recipients to check that the email was sent by the domain owner and hasn't been altered in transit. DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds on SPF and DKIM, providing instructions to receiving servers on how to handle emails that fail authentication, and offering valuable aggregate reports.
Setting up these records correctly is critical. Even a small misconfiguration can lead to deliverability issues. For example, if your SPF record has a DNS lookup error, your emails may fail authentication. If you're using an email service provider, make sure their instructions for setting up these records are followed precisely. It's also vital to ensure SPF and DKIM align with your DMARC policy, especially the domain in your From: header.
SPF record exampleDNS
v=spf1 include:_spf.example.com ~all
List hygiene and audience engagement
Your email list is your most valuable asset, and its quality directly impacts your deliverability and spam complaint rates. Sending to disengaged or invalid addresses can quickly lead to blocklists (or blacklists) and poor sender reputation. Implementing a double opt-in process for new subscribers is one of the most effective ways to ensure engagement and consent.
Regularly cleaning your email list is non-negotiable. Remove inactive subscribers who haven't opened or clicked your emails in a long time. These unengaged users can signal to ISPs that your content isn't wanted, which negatively affects your sender reputation. Also, actively identify and remove bounced emails, as high bounce rates hurt your sender score. Avoiding spam traps is crucial, as hitting them can instantly damage your standing.
A common mistake I see is marketers holding onto old data, hoping to re-engage them later. If a significant period has passed since subscribers opted in, they might have forgotten about you, leading to them marking your newsletter as spam. Consider a re-engagement campaign for older segments to confirm their interest before sending your regular content. This can help improve open rates and reduce complaints.
Healthy list practices
Double opt-in: Ensures explicit consent and reduces spam complaints from the start.
Regular cleaning: Removes inactive subscribers and invalid addresses.
Segmented sending: Targets content to engaged users, improving relevance.
Unhealthy list practices
Single opt-in: Can lead to unverified or uninterested subscribers.
Infrequent cleaning: Accumulates inactive users and spam traps, harming reputation.
Buying lists: Guarantees low engagement and high complaint rates.
Content quality and subscriber management
The content of your newsletter is a major factor in how subscribers perceive your emails and whether they hit the spam button. Mailbox providers analyze numerous elements within your email content to determine its legitimacy and relevance. This includes everything from the subject line to images, links, and even hidden text.
Avoid 'spammy' words, excessive punctuation, and all caps in your subject lines and body text. While these might grab attention, they are red flags for spam filters. Focus on providing value, being transparent about what your newsletter offers, and ensuring your content matches subscriber expectations. If users signed up for a specific report, don't immediately start sending them unrelated marketing material without clear communication.
Make it easy for subscribers to unsubscribe. A prominent, one-click unsubscribe link (List-Unsubscribe header) is crucial. If subscribers can't easily find how to opt-out, they're more likely to mark your email as spam, which is far worse for your reputation than an unsubscribe. A spam complaint rate above 0.10% can be detrimental. Regularly reviewing your spam complaint metrics helps you identify issues quickly. You can read more about email deliverability and its importance here.
Content dos and don'ts
Do: Provide clear value and relevant information.
Do: Personalize content where appropriate.
Do: Include a prominent, one-click unsubscribe link.
Don't: Use excessive caps, exclamation marks, or spam trigger words.
Don't: Include broken links or image-only emails.
Don't: Mislead with subject lines that don't match content.
Monitoring and reputation management
Proactive monitoring of your email deliverability metrics is key to catching issues before they escalate. Tools like Google Postmaster Tools (for Gmail) offer insights into your domain and IP reputation, spam rate, and authentication errors. Similarly, Outlook provides similar tools. Pay close attention to your spam complaint rate, aiming to keep it well below 0.3%.
Beyond monitoring, you need a strategy for managing your sender reputation. A sudden spike in spam complaints or a drop in engagement can signal a problem. When this happens, it's often more effective to pause your mailings to the affected segment, analyze the cause, and then re-engage with a strategy that focuses on value and confirmed interest. For more general advice on improving your email reputation, consider exploring dedicated guides.
Metric
Target Rate
Impact on deliverability
Spam complaint rate
<0.1% (ideally 0%)
High rates lead to blocklists & spam folder placement.
Bounce rate
<2%
High rates indicate poor list quality, harming reputation.
Strong indicator of subscriber interest and content relevance.
The path to better newsletter deliverability
Ensuring your newsletter reaches its audience and doesn't get flagged as spam requires a holistic approach. It’s a continuous process that involves technical setup, diligent list management, and delivering highly relevant content. By focusing on these areas, you can significantly improve your deliverability and maintain a positive sender reputation.
Remember, every email you send contributes to your sender reputation. Prioritize subscriber experience, be transparent, and consistently provide value. This dedication will ensure your newsletters avoid spam folders and foster long-term engagement with your audience.
Views from the trenches
Best practices
Use email authentication (SPF, DKIM, DMARC) to build trust with mailbox providers and verify sender identity.
Implement double opt-in to ensure subscribers genuinely want your newsletters and reduce initial spam complaints.
Regularly clean your email list by removing inactive subscribers and hard bounces to maintain good list hygiene.
Provide clear, valuable content that matches subscriber expectations to encourage positive engagement.
Ensure an easy-to-find, one-click unsubscribe link to prevent frustrated subscribers from marking emails as spam.
Common pitfalls
Ignoring email authentication, which can lead to emails failing DMARC alignment and being blocked.
Sending to old, unengaged, or unverified lists, resulting in high bounce and spam complaint rates.
Using misleading subject lines or content that doesn't align with what subscribers opted in for.
Making the unsubscribe process difficult, prompting users to report emails as spam instead of opting out.
Failing to segment your audience, leading to irrelevant content being sent to some subscribers.
Expert tips
Consider a re-engagement campaign for older segments who haven't received emails recently to confirm their interest.
If you experience high spam rates, reassess your audience and content strategy to send only what recipients truly want.
Understand that moving to a new domain won't fix underlying content or audience quality issues.
Keep your spam complaint rate below the recommended 0.3% threshold to avoid throttling or blocklisting by ISPs.
A gradual domain warm-up is essential for new domains to build a positive sending reputation over time.
Expert view
Expert from Email Geeks says a domain's reputation is shared across its subdomains, so focusing on improving the mail stream's overall reputation is generally more effective.
2024-06-18 - Email Geeks
Expert view
Expert from Email Geeks says a high complaint rate (e.g., 1.5%) indicates recipients do not want the mail. The solution involves rethinking the audience and sending content they truly desire, rather than changing domains.
Gmail) offer insights into your domain and IP reputation, spam rate, and authentication errors. Similarly, Outlook provides similar tools. Pay close attention to your spam complaint rate, aiming to keep it well below 0.3%.
