Why is Mailchimp client seeing sudden Gmail spam placement issues, and are other Mailchimp senders similarly affected?
Matthew Whittaker
Co-founder & CTO, Suped
Published 30 Apr 2025
Updated 17 Aug 2025
8 min read
Recently, I've heard from a client using Mailchimp who is experiencing a sudden shift of their emails to Gmail's spam folder. This kind of issue can be incredibly frustrating, especially when email campaigns have historically performed well. It immediately brings to mind the possibility of a broader problem, perhaps one affecting other Mailchimp senders as well.
When deliverability unexpectedly declines, particularly at a major inbox provider like Gmail, it often points to a few common culprits. These can range from changes in sending behavior to issues with the shared infrastructure of an email service provider (ESP). Understanding the nuances of how ESPs manage their sending reputation and how Gmail's filters interpret incoming mail is crucial for diagnosing such problems.
The immediate concern for any sender is whether their individual practices are at fault or if they are caught in a larger, systemic issue. This is especially pertinent when using a shared IP service. Let's delve into why these issues occur and what can be done to address them.
Understanding Mailchimp's shared IP environment
One of the primary factors when experiencing sudden deliverability issues with an ESP like Mailchimp is the nature of shared IP addresses. When you send through a platform like Mailchimp, your emails are delivered through their servers, often sharing IP addresses with many other users. This means the sending reputation of that shared IP (or IP pool) is an aggregate of all senders using it.
If even a few senders on the same shared IP engage in questionable practices, such as sending to unengaged lists, purchased lists, or generating high spam complaints, it can negatively impact the reputation of the entire IP. This collective degradation can lead to other legitimate senders, like your client, experiencing unexpected spam folder placement. Gmail's filters are sophisticated and can quickly identify problematic IP addresses, even if your individual sending practices are pristine.
Mailchimp typically manages its IP pools to mitigate this risk, often moving senders to different pools based on their reputation or behavior. However, this re-pooling can also inadvertently place a good sender on an IP that is currently under scrutiny by inbox providers, leading to a temporary dip in deliverability. Such shifts are not always immediately apparent to the end-user, making diagnosis more challenging.
Common causes of sudden Gmail spam placement
While shared IP issues can certainly contribute, it's also important to review the common factors that trigger Gmail's spam filters directly. These include sender reputation, content quality, and recipient engagement. Even if your client's prior campaigns were successful, small changes can lead to a sudden shift.
Sender reputation: This is Gmail's assessment of your sending domain and IP. Factors like spam complaints, bounce rates, and whether your emails are opened and clicked all contribute. A sudden increase in complaints, even from a small segment, can significantly hurt your reputation.
Content issues: Certain words, phrases, or formatting can trigger spam filters. Using deceptive subject lines, excessive use of exclamation points, or broken links can raise red flags.
List hygiene and engagement: Sending to unengaged subscribers, or worse, to spam traps, can severely damage your standing with inbox providers. Even a single spam trap hit can have disproportionate consequences.
Authentication issues: While Mailchimp handles much of this, ensure your domain's SPF and DKIM records are correctly configured and that DMARC is set up, even if it's on a relaxed policy. Misconfigurations or failures can lead to messages being filtered.
If you're facing this problem, a thorough review of your own sending practices is always the first step. Look for any recent changes in content, list acquisition methods, or sending frequency.
Client's potential impact
Sending content that appears generic, contains too many links, or includes problematic keywords, can trigger spam filters. Lack of consistent engagement (opens, clicks) from your audience also signals low interest, affecting deliverability.
List Quality: High bounce rates, spam complaints, or presence of spam traps indicate poor list hygiene, which directly impacts your sender reputation.
Engagement: Low open and click rates and high unsubscribe rates tell inbox providers that your content isn't wanted, leading to spam folder placement.
Diagnosing and troubleshooting deliverability issues
When sudden Gmail spam placement issues arise, a systematic approach to diagnosis is essential. My first step is always to verify foundational email authentication records like SPF, DKIM, and DMARC. Even if Mailchimp handles them, a manual check can reveal misconfigurations or recent changes to your DNS records. You can use a free online email testing tool to check these.
Next, I'd strongly recommend checking Google Postmaster Tools if your client has their domain verified there. This free tool provides invaluable insights into your domain's sending reputation with Gmail, including spam rate, IP reputation, domain reputation, and authentication errors. Spikes in the spam rate or drops in reputation scores can directly explain spam folder placement. You can also monitor your blocklist status or use a blacklist checker to see if you're on any blocklists (or blacklists).
Beyond technical checks, closely examine campaign-level metrics within Mailchimp. Look for any recent dips in open rates, increases in unsubscribe rates, or, critically, a rise in abuse complaints. Even a small increase in complaints can trigger spam filters. Segmenting your audience and sending to your most engaged subscribers first can help rebuild positive sending signals. Also, review your email content for any elements that could be perceived as spammy, such as excessive promotional language, image-to-text ratio, or broken links.
Mailchimp and broader deliverability trends
The question of whether other Mailchimp senders are affected is key to determining if the issue is isolated or widespread. While I can't speak for Mailchimp's internal operations, it's known that shared IP environments can sometimes experience collective reputation shifts. If multiple senders on the same IP pool are suddenly seeing deliverability issues, it points to a platform-level challenge rather than individual sender fault. This happened historically, and the concern is it could recur.
Major inbox providers like Gmail are continually refining their spam filtering algorithms. Recent changes emphasize strong email authentication (DMARC enforcement) and positive sender reputation, heavily influenced by user engagement metrics. This means even if Mailchimp is managing its IPs diligently, a collective downturn in sender quality across their user base could lead to aggregate issues for all clients on shared IPs.
This ongoing evolution of filtering standards means that what worked yesterday might not work today. Mailchimp, like all ESPs, must adapt to these changes. If they're experiencing a sudden, widespread drop, they will likely be working to identify and address the root cause, which might involve re-pooling IPs or enforcing stricter sending policies on problematic users.
Navigating deliverability challenges
Navigating deliverability challenges, especially when using a shared ESP like Mailchimp, requires both individual diligence and an understanding of the broader email ecosystem. While a sudden drop in Gmail inbox placement could be a symptom of a larger platform issue affecting Mailchimp's shared IP reputation, it’s equally important to rule out or address any issues specific to your client's sending practices.
Maintain rigorous list hygiene, ensure content is highly engaging and relevant, and monitor key metrics closely through tools like Google Postmaster. If these practices are sound and issues persist, then it's more likely that the problem lies with the shared IP environment. In such cases, direct communication with Mailchimp support, armed with your diagnostic data, is the next logical step. By staying proactive and informed, you can minimize the impact of these deliverability shifts.
Views from the trenches
Best practices
Maintain clean email lists by regularly removing inactive or unengaged subscribers to improve engagement rates.
Segment your audience and tailor content to ensure relevance, reducing spam complaints and increasing positive engagement.
Implement and monitor DMARC, SPF, and DKIM for your domain to ensure proper email authentication and build sender trust.
Leverage Mailchimp's audience engagement tools and campaign analytics to identify and address declining performance early.
Use Mailchimp's audience features to manage unsubscribes and preferences, giving recipients control over their email flow.
Common pitfalls
Ignoring low engagement metrics, which signals to ISPs that your emails are not valuable, leading to spam folder placement.
Sending to outdated or unverified email lists, increasing bounce rates and hits on spam traps.
Failing to monitor sender reputation metrics in tools like Google Postmaster Tools for early warning signs of issues.
Relying solely on Mailchimp's default settings for authentication without verifying your domain's full compliance.
Making significant changes to email content, frequency, or volume without gradually warming up the new sending pattern.
Expert tips
Actively monitor your sender reputation using free tools to catch potential issues before they escalate into widespread spam placement.
If using Mailchimp's shared IPs, understand that other senders' poor practices can affect your deliverability.
Focus on providing value in every email to encourage opens, clicks, and replies, which boosts your sender score.
Regularly test your email campaigns with various inbox providers to detect filtering issues proactively.
Implement a feedback loop process with major ISPs if possible, to automatically remove users who mark your emails as spam.
Marketer view
Marketer from Email Geeks says they noticed a large portion of Outlook spam placements recently for one of their clients.
2023-10-31 - Email Geeks
Marketer view
Marketer from Email Geeks says they suspect unwarranted or mostly unwarranted spam folder placement at Gmail today for their Mailchimp client.
