How to improve email deliverability with domain warm-up, reducing spam rates and managing unsubscribes?
Matthew Whittaker
Co-founder & CTO, Suped
Published 24 Apr 2025
Updated 16 Aug 2025
7 min read
Getting your emails to the inbox, rather than the spam folder, is a core challenge for any sender. It's not just about sending emails, it's about ensuring they land where they’re intended, fostering communication and engagement. This crucial aspect of email marketing is known as email deliverability.
Many factors influence whether your emails reach their destination, but three pillars stand out: establishing a solid sending reputation through domain warm-up, proactively reducing spam rates, and effectively managing unsubscribes. These elements are interconnected, and a misstep in one area can negatively impact the others, leading to reduced inbox placement.
A strong sender reputation is built on consistent positive engagement and adherence to best practices. Without it, your emails are more likely to be flagged by spam filters or blocked entirely, regardless of how valuable your content might be. This impacts your marketing efforts and the overall health of your email program.
In this guide, I'll walk you through how to master these critical areas to significantly improve your email deliverability, ensuring your messages consistently reach your audience.
The foundation of sender reputation: domain warm-up
Think of a new email domain or IP address as an unknown entity to mailbox providers like Gmail or Outlook. Domain warm-up is the strategic process of gradually increasing your email sending volume over time. This slow and steady approach allows mailbox providers to recognize your sending patterns, assess your engagement rates, and build a positive reputation for your domain. It’s a critical step, especially when setting up a new email sending domain.
Without proper warm-up, sending a large volume of emails from a new domain can immediately trigger spam filters. This can lead to your emails being marked as spam, blocked, or even land your domain or IP address on a blacklist (or blocklist). The goal is to demonstrate consistent, desired sending behavior and positive recipient engagement from the start.
The key is to start with your most engaged subscribers, those who are most likely to open and click your emails. Gradually, you can expand your audience and increase your daily sending volume. This process builds a strong foundation for your sender reputation, which is vital for long-term deliverability.Strategies for cold outreach will differ, but the principle of gradualism remains.
Day
Volume
Recipient Type
Notes
Days 1-3
50-100 emails/day
Highly engaged (recent opens/clicks)
Focus on positive engagement
Days 4-7
200-500 emails/day
Engaged (opened in last 30-60 days)
Monitor performance closely
Weeks 2-3
1,000-5,000 emails/day
Regular subscribers
Continue gradual increase
Weeks 4+
Gradual increase based on performance
Full list segments
Monitor spam rate and adjust
Tackling spam rates: content and engagement
A high spam rate is a direct signal to mailbox providers that your emails are unwanted. Even a seemingly small rate, like 0.5% to 1%, can be considered significant and detrimental to your sender reputation. When recipients mark your emails as spam, it severely impacts your ability to reach the inbox, potentially leading to your domain being put on a blacklist (or blocklist).
The problem with a high spam rate
A spam rate of even 0.5% to 1% signals to internet service providers (ISPs) that your mail isn’t desired by your recipients, regardless of how many people are on your list or how much you're sending. This isn't just a warm-up problem, it's a content and engagement issue that needs immediate attention before you can effectively scale your sending volume.
To reduce spam rates, focus on providing relevant, valuable, and engaging content. Personalize your emails where possible, segment your audience, and ensure your messaging aligns with recipient expectations. Content that feels like spam, or that users simply don't find useful, will consistently lead to complaints. For more in-depth strategies, explore expert tips to increase email deliverability.
Crucially, ensure your email authentication protocols are properly set up. This includes SPF, DKIM, and DMARC. These records verify that your emails are legitimately coming from your domain, preventing spoofing and improving trust with mailbox providers. A simple guide to DMARC, SPF, and DKIM can help you implement these.
Remember, the goal is to improve permission and send emails that recipients genuinely want to receive. If your emails are consistently going to spam, it signals deeper issues than just technical setup.
While it might seem counterintuitive, making it easy for subscribers to opt out of your emails is a powerful deliverability strategy. When recipients can easily unsubscribe, they are less likely to mark your emails as spam. A spam complaint carries a much heavier penalty for your sender reputation than an unsubscribe request.
Even for lower volume senders, implementing a clear and easily accessible unsubscribe link within the email body is a best practice. This helps maintain a clean, engaged email list and protects your sender reputation from unnecessary spam complaints. Recipients who no longer wish to receive your emails should be able to opt out effortlessly.
Prominent unsubscribe
Visibility: Placed clearly in the email header or at the top of the footer.
Impact: Reduces spam complaints by offering an easy exit, thus protecting your sender reputation.
Compliance: Aligns with Google and Yahoo's new sender requirements.
Hidden unsubscribe
Visibility: Small font, obscure placement, or multi-step process.
Impact: Frustrated recipients are more likely to mark as spam, damaging your reputation.
Risk: Increases the chance of landing on a blacklist (or blocklist) and deliverability issues.
Continuous monitoring and maintenance
Improving email deliverability is not a one-time setup, but an ongoing commitment. Continuously monitoring your email performance and domain reputation is essential to catch potential issues early and maintain strong inbox placement.
Utilize tools like Google Postmaster Tools to keep an eye on your spam rates, IP and domain reputation, and deliverability errors. Pay close attention to trends, not just individual metrics, to understand the trajectory of your email program. Also, regularly check if your IP or domain is listed on any email blocklists (or blacklists), as this is a clear sign of significant deliverability issues.
Regular list hygiene is also paramount. Remove inactive subscribers, hard bounces, and any addresses that have repeatedly soft bounced. A clean, engaged list will naturally improve your overall engagement rates and reduce the likelihood of spam complaints, contributing to a better sender reputation. If you've faced reputation challenges, a thorough cleanup is often the first step to recovery.
By proactively monitoring your metrics, performing regular list maintenance, and adapting your sending practices based on performance data, you can sustain high deliverability rates and ensure your email campaigns remain effective.
Views from the trenches
Best practices
Always warm up new domains or IP addresses with your most engaged data to build a positive sending reputation from the start.
Make unsubscribe options prominently visible and easy to use in your emails, especially the one-click unsubscribe, to reduce spam complaints.
Maintain consistent sending volumes rather than sporadic or irregular patterns, as this helps stabilize your sender reputation.
Prioritize list hygiene by regularly removing unengaged subscribers and bounced addresses to improve overall engagement and reduce risks.
Common pitfalls
Attempting to scale email volume when your domain already has a medium reputation and a 0.5-1% spam rate will worsen deliverability.
Failing to address high spam rates before increasing sending volume can lead to irreversible damage to your sender reputation.
Having a hidden or hard-to-find unsubscribe link that forces frustrated recipients to mark your emails as spam instead of opting out.
Sending to unengaged or poor-quality data during warm-up, which can pull down your domain's reputation and hinder progress.
Expert tips
Focus on improving recipient permission rather than trying to 'fix' spam rates by just removing complainers, especially with providers like Gmail.
Utilize clickers as the primary segment for initial warm-up, gradually introducing openers and less engaged contacts later and with caution.
Consider testing a more prominent unsubscribe link to clear out annoyed recipients, which can significantly reduce complaints.
Understand that even low spam complaint rates are significant indicators of recipient dissatisfaction and should be addressed promptly.
Expert view
Expert from Email Geeks says a spam rate of 1% with a medium domain reputation indicates that recipients perceive the mail as unwanted, and this isn't a warm-up issue, but rather a problem with meeting recipient expectations.
July 19, 2021 - Email Geeks
Marketer view
Marketer from Email Geeks says it is crucial to fix the spam rate before attempting to scale email volume further, as adding more data will likely reduce reputation.
July 19, 2021 - Email Geeks
Sustaining high deliverability
Achieving and maintaining high email deliverability is a complex, continuous process that requires attention to detail across multiple fronts. It begins with a strategic domain warm-up to build trust with mailbox providers, followed by a relentless focus on keeping spam rates low through relevant content and robust email authentication.
Equally important is empowering your recipients with easy unsubscribe options, which significantly reduces the likelihood of spam complaints and helps preserve your sender reputation. Finally, consistent monitoring and proactive list hygiene complete the picture, ensuring your email program remains healthy and effective over time.
By embracing these strategies, you can navigate the complexities of email deliverability, enhance your inbox placement, and foster stronger, more productive relationships with your audience.
Gmail or 
Outlook. Domain warm-up is the strategic process of gradually increasing your email sending volume over time. This slow and steady approach allows mailbox providers to recognize your sending patterns, assess your engagement rates, and build a positive reputation for your domain. It’s a critical step, especially when setting up a new email sending domain.
