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The Deliverability Download
Edition #6: The Building Blocks of Email Reputation

John Peters - Jun 23, 2025

In recent times (particularly since Google and Yahoo’s 2024 sender requirements), ‘email reputation’ has been a hot topic of conversation in email marketing. In our last edition of the Deliverability Download, we introduced the concept of email reputation and why it’s crucial to your deliverability success. Now it’s time to take a deeper dive – from permission-based lists to spam traps and domain authentication, this article breaks down the foundational elements that shape your sender reputation.

Building block 1: Permission-based opt-in

One of—if not the—most important elements, is sending to active, current subscribers who have given clear and explicit permission to be added to your list. This isn’t just a best practice, it’s also a legal requirement under many regional regulations, such as the Spam Act (AU), CAN-SPAM (US), and GDPR (EU). In addition, Campaign Monitor’s Anti-Spam Policy and Terms of Use often go above and beyond these legal baselines to ensure your recipients have a positive and respectful experience.

While gaining explicit permission is mandatory, it’s not necessarily evergreen, with subscribers always having the option to remove their consent or opt-out at any time. To help maintain opt-in permission, keep regular email contact with your subscribers, so they remember who you are, and why they signed up to your messages. Your list shouldn’t be made up of anyone you’ve emailed in the last couple of years. And, while this may sound strict, it helps ensure your engagement rates stay high and spam complaints stay low.

As Mailbox Providers (MBPs), like Gmail, Yahoo, and Outlook, use a range of signals to assign you a reputation, like recipient engagement, bounces, and spam complaints, if your emails are regularly ignored, deleted, or marked as spam by subscribers who no longer want to be opted-in, future messages are more likely to land in the junk folder or, worse, not be delivered at all.

Building block 2: Spam traps

If you’re sending to inactive or non-permission-based email addresses, you risk hitting spam traps, which are hidden addresses used to identify senders with poor list hygiene.

These traps are like ballast for your lists—they weigh you down and, if there are enough of them or if you start to encounter problems, they can pull you underwater.

Spam traps usually come from addresses that never gave permission, or ones where consent has long expired. Continually emailing them can even trigger blocks on shared IPs, which impacts not just you, but others using the same infrastructure.

Building block 3: Authentication (SPF, DKIM and DMARC)

Another critical building block of a strong sender reputation is setting up compliant domain authentication. SPF, DKIM, and DMARC, prove to receiving mail servers and your subscribers that you’re a legitimate sender.

However, it’s important to note that authentication alone doesn’t guarantee a good reputation; even spammers can authenticate, but it’s a prerequisite for building trust. It prevents spoofing (bad actors online pretending to be you), protects your brand, and is now mandatory with most major MBPs like Gmail, Yahoo, and Microsoft, with each step in the authentication process playing a different, yet vital role:

• SPF and DKIM help verify that your emails are genuinely from you, while
• DMARC gives you control over how your domain is treated when authentication checks fail

Authentication: A simple analogy

Here’s a simple analogy to explain how SPF, DKIM, and DMARC work together. Imagine you’re trying to get into an exclusive VIP event. Security is tight, the organisers want to verify your identity, and only guests from known and trusted companies are allowed in. To gain entry, security checks a few different things:

• SPF is like arriving in an official company car. Security checks a list to see if your company has approved that car to transport guests. If it’s on the list, that’s a good sign.
• DKIM is like holding a verified invitation with your company’s name and signature. Security inspects it to make sure it isn’t fake.
• DMARC tells security what to do based on your company’s policy. It says:

If the guest passes at least one of these checks (either the vehicle or the invitation), and it matches our records, let them in. If not, here’s what to do:

• disregard the security checks (other filters still apply),
• send them to the holding area (spam)
• or deny them entry (reject/not delivered)

But even if you pass the ID checks and your invitation looks perfect, your past behavior matters. If you’ve caused problems at past events, security might still be suspicious or deny entry. To put it simply, authentication proves your identity and reputation determines how you’re treated.

Six easy steps to build your sender reputation

While we’ve covered the foundational elements, here are some actionable steps you can take right now to boost your sender reputation:

1. ​​Audit your lists regularly: Remove long-term inactive subscribers every 3–6 months. They’re unlikely to re-engage and may be spam traps or abandoned inboxes.
2. Implement a sunset policy: Use automation to identify fading engagement and either re-engage or remove subscribers after a set period.
3. Start small with new segments: Add new audience groups gradually, especially if sourced through new channels or showing different engagement patterns.
4. Monitor bounce rates: Act fast on hard bounces, and remove them immediately from your database if stored and sync your lists outside Campaign Monitor. Persistent high bounce rates can severely damage your reputation.
5. Authenticate everything: Ensure SPF, DKIM, and DMARC are correctly set up. These are now the minimum requirements for email deliverability.
6. Use double opt-in: Confirm new subscribers with a verification email to ensure list quality from day one, and use our secure signup forms to collect emails safely.

Getting these basics right creates a solid foundation for your email program.

Foundation first, results next

Permission-based lists, avoiding spam traps, and proper authentication are the backbone of your sender reputation. Without them, even the best-crafted content won’t reach your subscribers’ inboxes.

Get these basics right first, then shift your focus to what truly drives results: subscriber engagement.

This is the second article in our three-part series on Email Reputation. Keep an eye out for next month’s Deliverability Download, “Engagement Drives Reputation: How to Track and Improve It” as we’ll explore how engagement influences your reputation and how to effectively monitor it across mailbox providers.