How to improve email IP and domain reputation and what to audit for deliverability?
Matthew Whittaker
Co-founder & CTO, Suped
Published 29 Jul 2025
Updated 19 Aug 2025
8 min read
Email deliverability is a complex landscape, and at its core lies your IP and domain reputation. These two elements are critical, influencing whether your emails land in the inbox, the spam folder, or simply disappear into the void. For many, understanding and improving this reputation can feel like navigating a maze, especially when things go wrong and you are trying to understand what went wrong. I have seen situations where organizations mistakenly used their corporate email for marketing, leading to a severely damaged IP reputation, despite best efforts to correct course later.
This challenge highlights a fundamental truth: maintaining a healthy sender reputation requires ongoing vigilance and a deep understanding of the underlying mechanisms. It's not just about stopping bad practices, but actively fostering good ones to rebuild trust with mailbox providers. Even if your domain starts showing signs of improvement, a poor IP reputation can still hold you back.
The path to better deliverability often starts with a comprehensive audit. This means thoroughly examining your current sending infrastructure, authentication, content, and recipient engagement. Without a clear picture of what's happening, improving your email deliverability is often a shot in the dark.
Understanding IP and domain reputation
Your IP and domain reputation are essentially scores that mailbox providers like Google and Outlook assign to your sending entities. These scores dictate how likely your emails are to be accepted and delivered to the inbox. A strong reputation signals to ISPs that you are a legitimate sender, while a poor one flags your emails as suspicious or undesirable.
An IP reputation is tied to the specific internet protocol address from which your emails originate. If this IP address has been used for spamming or other abusive activities in the past, its reputation will suffer, regardless of your current sending practices. Conversely, domain reputation is linked to your sending domain name. This score considers factors like spam complaints, bounce rates, recipient engagement, and whether your domain appears on blocklists.
Shared IP addresses can complicate reputation management, as your deliverability can be impacted by the sending habits of others using the same IP. If your operational emails are on a shared IP that is being abused, it can significantly hinder your inbox placement. This is why understanding your email hosting setup, whether it's on-premises or managed by a third party, is crucial.
One primary way to gauge your standing is through tools like Google Postmaster Tools. This provides insights into your IP and domain reputation, spam rates, and delivery errors. Regularly checking these metrics is fundamental to proactive reputation management.
Essential authentication protocols
Email authentication protocols are the bedrock of good sender reputation. SPF, DKIM, and DMARC work together to verify that your emails are legitimate and that they haven't been tampered with in transit. Without these in place, even well-intentioned emails can appear suspicious to receiving servers. I've seen countless instances where missing or misconfigured authentication was the root cause of deliverability issues.
SPF (Sender Policy Framework) allows receiving mail servers to check that an email claiming to come from a specific domain is sent from an IP address authorized by that domain's administrators. DKIM (DomainKeys Identified Mail) provides a way to digitally sign your emails, allowing recipients to verify that the email was indeed sent by the domain owner and that its content hasn't been altered. DMARC (Domain-based Message Authentication, Reporting, & Conformance) builds on SPF and DKIM, telling receiving servers what to do with emails that fail authentication and providing valuable reports on your email stream.
Ensuring these protocols are correctly configured is non-negotiable for improving your reputation. For example, if DKIM signing stops working, as I've observed in some scenarios, it can severely impact your domain's ability to build trust. Regularly reviewing your DNS records for SPF, DKIM, and DMARC is a critical step in any deliverability audit. You can use a free DMARC record generator tool to ensure your records are syntactically correct.
Here’s an example of a simple DMARC record you might start with:
Phishing protection: DMARC helps protect your brand from spoofing and phishing attacks by ensuring only authorized senders use your domain.
Visibility: DMARC reports provide invaluable data on who is sending email using your domain, helping you identify unauthorized senders and authentication failures.
Content and engagement factors
Beyond the technical setup, the content of your emails and how recipients engage with them play a massive role in your IP and domain reputation. Mailbox providers closely monitor engagement signals, such as opens, clicks, and replies, as well as negative signals like spam complaints and unsubscribes.
Maintaining a clean and engaged email list is paramount. Sending to unengaged users or invalid addresses can lead to high bounce rates and spam trap hits, which are detrimental to your reputation. Implementing double opt-in for new subscribers and regularly cleaning your list of inactive users can significantly mitigate these risks.
The content itself should be relevant, valuable, and free of spammy trigger words or excessive images. Personalization and segmentation can help ensure your messages resonate with your audience, leading to higher engagement and fewer complaints. Remember, good email sending practices are essential for building and maintaining a positive domain reputation.
Consider these best practices for optimizing your email content:
Audience segmentation: Tailor content to specific segments to improve relevance and engagement.
Engagement tracking: Monitor open rates, click-through rates, and reply rates to gauge content effectiveness.
Feedback mechanisms: Encourage replies and provide clear unsubscribe options to minimize spam complaints.
Conducting an email deliverability audit
When facing reputation challenges, a detailed email deliverability audit is your most effective tool. This involves systematically reviewing every aspect of your email sending infrastructure and practices. My initial step is always to verify basic technical configurations, particularly how the IPs are authenticated.
Beyond authentication, an audit should delve into the specifics of your sending IPs. Are you using dedicated or shared IPs? If shared, understanding the reputation of other senders on that IP is crucial, as their bad practices can negatively affect yours. You also need to examine whether your IP is listed on any blocklists. Being on a major blacklist can severely disrupt your email delivery.
A full audit also means looking at your email sending volume, consistency, and how you handle bounces and complaints. High bounce rates signal a poor list, while frequent complaints indicate that your content is not wanted. I always recommend using tools to accurately test and measure your deliverability.
Key audit areas
A thorough audit should cover both technical and policy aspects to pinpoint the root causes of deliverability issues.
Email headers: Examine email headers for correct rDNS, HELO values, and MailFrom addresses.
IP address types: Determine if you're using dedicated or shared IPs, and assess their impact on your reputation.
Blocklist status: Check major blocklists (blacklists) for any listings of your IPs or domains.
Technical audit items
Sending MTA: Identify the mail transfer agent (MTA) used and check its configuration for limits and retry periods.
Bounce handling: Ensure your system correctly processes deferred and permanent rejections, removing invalid addresses.
Abuse addresses: Verify that your abuse address is active and forwards complaints to the right place.
Views from the trenches
Best practices
Actively monitor engagement metrics like open and click rates, as positive engagement boosts reputation.
Segment your email lists based on recipient behavior and preferences to ensure relevance.
Implement double opt-in for all new subscribers to confirm their genuine interest and reduce spam complaints.
Regularly clean your email lists by removing inactive subscribers and hard bounces to maintain hygiene.
Ensure SPF, DKIM, and DMARC are correctly configured and actively maintained for all sending domains.
Consider warming up new IP addresses or domains gradually to build a positive sending history.
Common pitfalls
Sending emails to purchased or old, unverified lists, which often contain spam traps or invalid addresses.
Ignoring spam complaints or high bounce rates, as these severely damage sender reputation.
Using generic or free email hosting for professional or marketing emails, lacking necessary authentication features.
Failing to monitor blacklists (or blocklists), leading to unawareness of major deliverability issues.
Not having a clear strategy for re-engaging or removing inactive subscribers, which can drag down engagement metrics.
Sending inconsistent email volumes, which can flag your sending patterns as suspicious to ISPs.
Expert tips
Always prioritize recipient engagement and list hygiene; a good sender reputation stems from sending wanted emails.
Investigate any changes in deliverability promptly, using DMARC reports and diagnostic tools.
Understand the difference between dedicated and shared IP addresses and choose the right setup for your sending volume.
For complex setups, don't hesitate to consult with your CTO or an email deliverability specialist.
Continuously educate yourself on evolving email standards and ISP requirements to stay ahead of deliverability challenges.
Implement a feedback loop (FBL) system with major mailbox providers to receive spam complaint data directly.
Expert view
Expert from Email Geeks says: I generally start with technical aspects when auditing clients, including what IPs are used, how they are authenticated via SPF/DKIM, and examining headers for rDNS and consistent HELO values.
2019-10-02 - Email Geeks
Expert view
Expert from Email Geeks says: It's important to understand your sending MTA, how limits are configured, how deferred mail is handled, and when to drop addresses from your list.
2019-10-02 - Email Geeks
The path to better deliverability
Improving your email IP and domain reputation, and ensuring strong deliverability, is an ongoing process that demands attention to both technical configurations and sending practices. It’s a journey that involves understanding how mailbox providers evaluate your emails, meticulously setting up authentication protocols, and consistently sending valuable, relevant content to engaged recipients.
A comprehensive audit is the starting point, providing the insights needed to identify weaknesses and formulate a strategy. By prioritizing authentication, maintaining list hygiene, and monitoring your sender reputation diligently, you can foster the trust required to ensure your emails consistently reach the inbox. This commitment to best practices is ultimately what drives long-term email marketing success.
