How does email deliverability work in the current email marketing landscape?
Matthew Whittaker
Co-founder & CTO, Suped
Published 30 May 2025
Updated 19 Aug 2025
7 min read
Email deliverability is the cornerstone of effective email marketing. It's not enough to simply send emails; they must land in the recipient's inbox. In today's dynamic email landscape, understanding how deliverability works is more complex than ever before, with significant changes occurring over recent years.
Mailbox providers, such as Gmail and Outlook, continuously evolve their filtering technologies to combat spam and protect users. This means the rules of the game are always shifting, making it challenging for marketers to ensure their messages consistently reach the intended audience.
Success hinges on a multifaceted approach, blending technical compliance with user-centric content strategies and ongoing vigilance. I'll explain how these elements interact to determine your email's ultimate destination.
Sender reputation and trust
At the core of deliverability is your sender reputation. This is a crucial score that mailbox providers assign to your sending IP address and domain, based on your historical sending behavior. A strong reputation signals that you are a legitimate sender, which significantly increases your chances of inbox placement. Conversely, a poor reputation can lead to emails being sent directly to the spam folder or even blocked entirely.
Many factors contribute to your sender reputation. High complaint rates, excessive bounces, and sending to inactive or invalid addresses are major red flags. Landing on a public or private blacklist (also known as a blocklist) is another clear indicator of poor sending practices and will severely impact your ability to reach inboxes. You can learn more about how sender reputation factors influence deliverability and how your email tool affects it.
Building and maintaining a positive reputation requires consistent adherence to best practices, focusing on sending desired content to engaged recipients. It’s a long-term investment, not a quick fix.
Bad reputation indicators
High complaint rates: Many recipients marking your emails as spam.
Excessive bounces: Sending to invalid or non-existent email addresses.
Spam trap hits: Sending to dormant or repurposed email addresses used to identify spammers.
Blocklist listings: Your IP or domain appearing on a public email blacklist (blocklist).
Good reputation indicators
High open rates: Recipients consistently opening your emails.
Strong click-through rates: Recipients clicking links within your emails.
Replies and forwards: Indicates genuine interest and engagement.
Low unsubscribe rates: Recipients prefer to stay subscribed.
Technical authentication foundations
Beyond reputation, robust technical authentication is non-negotiable in the current email landscape. Protocols like SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance) work together to verify that your emails are legitimate and haven't been tampered with. These are essential signals that mailbox providers use to trust your messages, directly impacting if your emails hit the inbox instead of spam.
SPF allows you to specify which mail servers are authorized to send email on behalf of your domain. DKIM adds a digital signature to your outgoing emails, verifying that the email content hasn't been altered during transit. DMARC builds upon SPF and DKIM, giving you control over how mailbox providers should handle emails that fail authentication, and provides valuable reporting on your email streams. A simple guide to DMARC, SPF, and DKIM can help you understand these protocols.
With new requirements from major mailbox providers, such as those announced by Google and Yahoo in 2024, implementing a DMARC policy with enforcement (p=quarantine or p=reject) is becoming mandatory for many senders. Failure to do so can lead to significant deliverability issues, as your emails may be treated as suspicious or outright rejected. You can learn how to comply with Outlook's new sender requirements for further guidance.
Example DMARC record for enforcement
This DMARC record specifies a policy of quarantine, meaning emails failing DMARC authentication will be placed in the recipient's spam folder. It also sends aggregate reports to dmarc-reports@yourdomain.com.
While technical setup and reputation are foundational, user engagement is arguably the most dynamic and influential factor in modern email deliverability. Mailbox providers closely monitor how recipients interact with your emails, using signals like opens, clicks, replies, and forwarding as positive indicators. Conversely, unsubscribes, marking as spam, or simply deleting without opening send negative signals.
This means the content of your emails must be relevant, valuable, and personalized. Generic, mass-blast emails are far less likely to land in the inbox than targeted, segmented messages that resonate with the recipient. The old "send to everyone" mentality is a recipe for deliverability disaster. The focus should be on relevant content that your subscribers genuinely want to receive. You can optimize your content using email testing best practices.
Maintaining a clean and engaged email list is paramount. Regularly removing inactive subscribers and avoiding purchased lists can prevent spam trap hits and reduce bounce rates, both of which severely harm your sender reputation. Quality over quantity is the golden rule, ensuring your emails reach those who genuinely want to receive them. Your sending frequency also plays a role. Too many emails can lead to fatigue and increased complaints, while too few might cause recipients to forget they subscribed. Finding the right balance is key to fostering sustained positive engagement.
Signal type
Positive engagement
Negative engagement
Recipient actions
Opens, clicks, replies, forwards, moving to primary inbox
Deletes without opening, marking as spam, moving to trash
The email marketing landscape is constantly evolving, with mailbox providers regularly updating their algorithms and policies. What worked last year might not work today. This dynamic environment necessitates a proactive approach to email deliverability, where continuous monitoring and swift adaptation are key to sustained inbox placement, as noted by industry discussions.
Relying solely on open rates as a measure of success is insufficient; you need to understand where your emails are actually landing. This involves using various tools, including Postmaster Tools provided by GoogleYahoo to gain insights into your sender reputation, spam rates, and delivery errors. Regularly checking for your IP and domain on various blacklists (or blocklists) is also crucial. For more details, explore this in-depth guide to email blocklists.
When deliverability issues arise, prompt troubleshooting and corrective action are essential. Whether it's a sudden spike in bounce rates, a drop in inbox placement, or a blacklist listing, identifying the root cause quickly and implementing solutions, such as list cleaning or adjusting sending volume, can mitigate long-term damage. This ongoing vigilance ensures your email program remains healthy and effective. Discover how to monitor email deliverability effectively.
Proactive monitoring strategies
Daily checks: Monitor spam rates and reputation scores in Postmaster Tools.
Blocklist (blacklist) vigilance: Regularly check if your IPs or domains are listed on major blocklists.
Feedback loops (FBLs): Enroll in FBLs to receive notifications when recipients mark your emails as spam.
DMARC reports: Analyze DMARC aggregate and forensic reports to identify authentication issues.
Bounce tracking: Pay attention to soft and hard bounce rates to maintain list hygiene.
Views from the trenches
Best practices
Maintain a clean and highly engaged email list by regularly removing inactive subscribers.
Implement strong email authentication (SPF, DKIM, DMARC) to build trust with mailbox providers.
Segment your audience and personalize content to ensure relevance and boost engagement.
Monitor your sender reputation continuously using tools like Google Postmaster Tools.
Respond quickly to any deliverability issues, such as blocklist listings or high spam rates.
Common pitfalls
Sending emails to purchased or old, unengaged lists, which leads to spam traps and bounces.
Ignoring email authentication protocols, making your emails appear suspicious to filters.
Focusing solely on quantity over quality, leading to generic and irrelevant content.
Neglecting to monitor deliverability metrics, missing early warning signs of issues.
Failing to adapt to evolving mailbox provider rules and sender requirements.
Expert tips
Consider deliverability a continuous process, not a one-time setup, requiring ongoing optimization.
Prioritize user experience: emails that recipients genuinely want will almost always reach the inbox.
Educate internal stakeholders on the importance of deliverability beyond just marketing metrics.
A proactive approach to list management can prevent many deliverability problems before they start.
Diversify your sending strategy to avoid over-reliance on a single IP or domain for critical emails.
Expert view
Expert from Email Geeks says: Deliverability is not about an instant outcome, but a result built over time through consistent, positive sending practices.
2019-05-08 - Email Geeks
Expert view
Expert from Email Geeks says: In the simplest terms, deliverability relies on engagement, although the definition of engagement is constantly evolving, making it a moving target.
2019-05-08 - Email Geeks
Navigating the inbox successfully
Achieving strong email deliverability in today's landscape requires a holistic and adaptive strategy. It's no longer just about getting past a simple spam filter; it's about building and maintaining trust with mailbox providers and, most importantly, with your subscribers. The complexities of email deliverability mean that success in the current email marketing landscape hinges on staying informed and proactive.
By prioritizing sender reputation, ensuring technical compliance with authentication protocols, focusing on genuine user engagement through valuable content, and continuously monitoring your performance, you can significantly improve your chances of consistently reaching the inbox. This commitment to best practices will safeguard your email marketing efforts and ensure they remain effective for years to come.
Gmail and 
Outlook, continuously evolve their filtering technologies to combat spam and protect users. This means the rules of the game are always shifting, making it challenging for marketers to ensure their messages consistently reach the intended audience.
Google
Yahoo to gain insights into your sender reputation, spam rates, and delivery errors. Regularly checking for your IP and domain on various blacklists (or blocklists) is also crucial. For more details, explore this in-depth guide to email blocklists.
