Case Study: How Mailchimp Restored Email Deliverability After Blacklist Issues
See how Mailchimp tackled email blacklist challenges, restored deliverability, and rebuilt trust. Learn lessons to apply to your own campaigns.
When Even the Big Guys Get Blacklisted
You might think blacklisting only happens to small senders or shady spammers — but that’s not the case. Even well-established platforms like Mailchimp have run into blacklist issues. The difference? How they handled it. 👀
In this case study, we’ll explore how Mailchimp faced a deliverability crisis, took swift action, and emerged stronger — with important takeaways that you can apply to your own email strategy, whether you're running campaigns for a startup or scaling a SaaS product 🚀.
The Challenge: High Volume, Higher Scrutiny
As one of the world’s largest email service providers (ESPs), Mailchimp sends billions of emails every month. With that kind of volume comes a magnifying glass from spam filters and blacklist operators.
In 2021, Mailchimp’s shared IP pool faced a sudden spike in spam complaints and bounce rates due to several users violating their acceptable use policies (AUPs). A few bad actors caused shared IPs to get flagged, impacting deliverability across multiple customer accounts.
The result?
Emails routed straight to spam 🗑️
Lower sender scores across key domains
A dip in client trust and performance metrics
The Fix: Cleaning House (Fast)
Mailchimp’s deliverability team launched an immediate response plan. And spoiler: it worked. Here's what they did — and what you can learn from it:
🔍 1. Identified the Root Cause
Mailchimp analyzed their sending logs and isolated accounts with:
High bounce rates 📉
Excessive spam complaints
Poor list hygiene
Once the culprits were found, they were either warned, suspended, or removed to stop the bleeding.
💡 Takeaway for You:
If your deliverability dips, don’t guess — audit your sends. Look for spikes in bounces, complaints, or sudden engagement drops.
🧼 2. Cleaned the Sending Infrastructure
They moved impacted accounts to clean IPs, updated sending practices, and re-verified list quality across affected users.
They also:
Enhanced internal spam filtering
Strengthened compliance checks before campaigns went live
Tightened their SMTP monitoring and response protocols
💡 Takeaway for You:
Use clean IPs or rotate domains when your sender reputation drops. And verify your list before every upload (especially if you’re running cold email or B2B outreach).
🛡️ 3. Reinforced Email Authentication
To prevent future issues, Mailchimp made SPF, DKIM, and DMARC setup mandatory for new domains.
This ensured mailbox providers could trust the legitimacy of emails sent through their platform.
💡 Takeaway for You:
If you’re not using SPF, DKIM, and DMARC, you’re vulnerable to spoofing and blacklisting. Get those records in place — today.
💡 With SenderWiz, setting up SPF/DKIM is a guided, user-friendly process — no need to dig through DNS settings alone.
📣 4. Improved Communication with ISPs and Blacklist Operators
Mailchimp proactively contacted blacklist operators (like Spamhaus and Barracuda) with:
Incident reports
Corrective actions taken
Future prevention plans
This accelerated their delisting and rebuilt trust with inbox providers.
💡 Takeaway for You:
When requesting removal from a blacklist, show that you’re serious. Be transparent, share what went wrong, and what you’ve done to fix it.
📊 5. Rolled Out Better Monitoring Tools
Post-blacklist, Mailchimp doubled down on:
Real-time alert systems for bounce or complaint spikes
Improved feedback loop management
Enhanced email engagement tracking
These tools helped them catch issues before they escalated.
💡 Takeaway for You:
Don’t fly blind. Use analytics and monitoring tools to track bounce rates, open rates, and spam complaints.
📌 With SenderWiz, you can track campaign health at a glance — including open rates, replies, bounces, and delivery success, all from one dashboard.
The Result: Deliverability Recovered — and Then Some
Within weeks of the blacklist event, Mailchimp:
Had their IPs delisted
Restored inbox placement with Gmail, Yahoo, and Microsoft
Improved their sender score beyond pre-blacklist levels
Regained customer trust through transparency and updates
More importantly, they emerged with a stronger infrastructure, better customer education, and tightened compliance policies to prevent a repeat.
Final Thought: Bounce Back Stronger
Even the most respected platforms can get blacklisted. What matters is how you respond, how fast you fix, and how well you learn from the situation.
With a tool like SenderWiz, you can take control of your sending infrastructure, track performance in real-time, automate authentication, and ensure your emails are hitting the inbox — not the blacklist.
🚀 Keep your sender reputation clean, your list engaged, and your campaigns firing on all cylinders.
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