What steps can I take to resolve email deliverability issues and improve my sender reputation?
Matthew Whittaker
Co-founder & CTO, Suped
Published 8 Jun 2025
Updated 16 Aug 2025
5 min read
Email deliverability challenges can be incredibly frustrating, especially when you are confident you are not sending spam yet your emails are not reaching the inbox. Many factors can influence whether your messages land in the primary inbox, the spam folder, or are blocked entirely. Understanding these factors and proactively managing them is crucial for maintaining a strong sender reputation and ensuring your email campaigns succeed.
When facing deliverability issues, it is not always immediately clear what caused the problem. Sometimes, a sudden drop in open rates or an increase in bounce notifications can indicate a deeper underlying issue with your sender reputation. Recovering from such issues requires a systematic approach, addressing both technical configurations and content-related aspects of your email program.
Email authentication essentials
One of the most critical steps to resolving email deliverability issues is to establish and maintain robust email authentication. SPF, DKIM, and DMARC are the pillars of email security and play a significant role in how mailbox providers view your sending domain. Without proper authentication, your emails are more likely to be flagged as suspicious or spam, regardless of their content.
Sender Policy Framework (SPF) allows you to specify which mail servers are authorized to send email on behalf of your domain. DomainKeys Identified Mail (DKIM) adds a digital signature to your outgoing emails, verifying that the email has not been tampered with in transit. Domain-based Message Authentication, Reporting, and Conformance (DMARC) builds on SPF and DKIM, telling receiving servers what to do with emails that fail authentication and providing valuable feedback reports.
Ensuring these records are correctly configured is paramount. A misconfigured SPF record, for example, could lead to legitimate emails failing authentication. Similarly, issues with your DKIM signature can cause delivery problems. DMARC, when implemented correctly, helps to enforce these policies and protect your domain from impersonation, a common cause of reputation damage. For instance, a DMARC record might look something like this:
If your emails are being blocked, checking your DMARC record and reports can often reveal why. You can gain valuable insights into authentication failures and potential abuse of your domain. This information is key to improving your email sender reputation.
Regularly monitoring your DMARC monitoring is a proactive measure that helps you identify and fix authentication issues before they severely impact deliverability. Similarly, keeping an eye on your blocklist monitoring status ensures you are aware if your domain or IP gets listed, allowing for swift action.
Maintaining a healthy email list
The health of your email list directly impacts your sender reputation and deliverability. Sending to invalid, inactive, or unengaged addresses can lead to high bounce rates and spam complaints, signaling to mailbox providers that your sending practices are poor. This can cause a rapid decline in your sender reputation and lead to your emails being directed to the spam folder or even blocked.
Implementing a double opt-in process for new subscribers is one of the most effective ways to ensure list quality. This requires subscribers to confirm their subscription, preventing mistyped addresses and malicious sign-ups (known as email list bombing). Regularly cleaning your list by removing inactive subscribers, hard bounces, and addresses that frequently mark your emails as spam is also vital. Inactive subscribers, in particular, can be a sign of low engagement, which negatively impacts your reputation.
Good practices
Double opt-in: Require subscribers to confirm their email address.
List cleaning: Regularly remove hard bounces and unengaged users.
Segmenting: Send targeted content to engaged segments.
Bad practices
Purchased lists: Avoid buying or renting email lists.
Spam traps: Sending to these will severely damage your reputation.
Single opt-in only: Increases risk of bad data and complaints.
Paying attention to your bounce rates is crucial. A sudden spike in bounces, particularly hard bounces, often indicates an issue with list quality or a block by an internet service provider (ISP). These issues, if not addressed quickly, can significantly impact your overall email reputation. Mailbox providers like Gmail and Outlook heavily weigh these metrics when determining where your emails should land.
Optimizing your sending strategy
Beyond technical configurations and list hygiene, the content of your emails and your sending patterns significantly influence deliverability. Mailbox providers analyze email content for spammy keywords, suspicious links, and image-to-text ratios. Crafting engaging, relevant, and well-formatted content can improve engagement metrics, which in turn boosts your sender reputation.
Consider your sending volume and consistency. If you are using a new IP address or have not sent emails in a while, it is crucial to warm up your IP by gradually increasing your sending volume over time. Sudden spikes in volume can trigger spam filters. Aim for a consistent sending schedule to build a predictable reputation with ISPs.
Good content practices
What to avoid
Personalized and relevant content
Spammy keywords or excessive capitalization
Clear and concise subject lines
Too many images, too little text
Obvious unsubscribe links
Ambiguous or hidden unsubscribe options
Monitoring engagement metrics, such as open rates, click-through rates, and unsubscribe rates, provides valuable insights into how your audience perceives your emails. Low engagement and high complaint rates can quickly degrade your sender reputation, making it harder to reach the inbox. If you find your email deliverability declining, analyzing these metrics is a key diagnostic step. You can also leverage tools like Google Postmaster Tools for reputation insights.
Views from the trenches
Best practices
Always use a double opt-in process to build a clean and engaged email list from the start.
Regularly monitor your bounce rates and remove invalid or inactive email addresses to maintain list hygiene.
Implement SPF, DKIM, and DMARC to authenticate your email domain and protect your sender reputation.
Segment your audience and send targeted content to improve engagement and reduce spam complaints.
Warm up new IP addresses or domains by gradually increasing sending volume over several weeks.
Common pitfalls
Using single opt-in processes which can lead to invalid email addresses and spam traps.
Neglecting to clean your email list, resulting in high bounce rates and low engagement.
Failing to implement SPF, DKIM, or DMARC, leaving your domain vulnerable to spoofing and poor deliverability.
Sending inconsistent email volumes, which can confuse mailbox providers and trigger spam filters.
Ignoring engagement metrics, leading to a decline in sender reputation and poor inbox placement.
Expert tips
Investigate any high bounce days to identify the root cause, such as a compromised signup form.
Consider the long-term cost of not reaching major mailbox providers like Gmail if product changes are resisted.
Review your signup process for vulnerabilities like the absence of CAPTCHA or honeypot fields.
Delay asking for email addresses in surveys until the end, and make it optional to improve data quality.
Focus on engagement and severely reduce sending volume in the short term to recover from deliverability issues.
Expert view
Expert from Email Geeks says to check if you are on a shared or dedicated IP and to access your bounce logs. Gmail does not block based on a SORBS listing but on its own metrics, which often relate to list hygiene.
2022-09-01 - Email Geeks
Expert view
Expert from Email Geeks says that if Google is blocking your mail, it is likely because their users have marked your emails as unwanted, indicating that your list quality and email acquisition methods need attention.
2022-09-01 - Email Geeks
Consistent effort for lasting success
Improving email deliverability and sender reputation is an ongoing process that requires diligent effort across technical setup, list management, and content strategy. There is no quick fix, but by focusing on these key areas, you can significantly enhance your chances of reaching the inbox consistently.
Remember, a strong sender reputation is like a credit score for your email program, built on trust and consistent positive behavior. By prioritizing authentication, maintaining a clean and engaged list, and sending valuable content, you pave the way for successful email delivery.
Gmail and 
Outlook heavily weigh these metrics when determining where your emails should land.
