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Email marketing remains one of the most effective tools in a digital marketer’s arsenal. However, many founders and companies have learned the hard way that even the best-designed marketing suites can inadvertently trigger spam filters and hurt sender reputation. With email service providers (ESPs) tightening spam detection protocols, the consequences of poor practices can range from blacklists to serious drops in deliverability rates.
TL;DR
Marketing automation tools can sometimes backfire if misused, especially when aggressive tactics or poor list hygiene leads to spam complaints and sender blacklisting. This article explores nine popular all-in-one marketing suites that experienced such issues — and more importantly, how their founders rectified the problem. From rewriting sender policies to investing in stricter list validation, they took bold steps to rebuild their email reputation. Their lessons are essential reading for marketers aiming to maintain peak email deliverability.
1. ActiveCampaign – Automated Triggers Gone Wild
ActiveCampaign is famous for its deep automation capabilities. Unfortunately for one software startup, they went overboard with conditional email paths, firing off 8–10 emails to new leads in under 48 hours. The tactic overwhelmed recipients, spiked complaint rates, and landed them on several domain blacklists.
Solution: The founders slowed down the automation flow and added engagement-based triggers. They also implemented a double opt-in and began warming new IP addresses gradually to restore sender reputation.
2. Mailchimp – Cold Outreach Misunderstood
As a trusted name in email marketing, Mailchimp has clear policies against cold emailing. Yet a real estate SaaS platform uploaded a purchased list into their account, assuming Mailchimp’s strong deliverability would cover them. Within days, they were flagged for violations and suspended.
Solution: After switching to a more flexible provider for cold outreach, they returned to Mailchimp for warm, in-house contacts only. They also educated their team on compliance and created SOPs for list hygiene.
3. HubSpot – CRM Overload Leading to Spam Complaints
HubSpot’s tight integration between CRM data and email marketing enabled one B2B company to scale quickly. But their mistake was nurturing unrelated leads with irrelevant email content for months, leading to high unsubscribe and complaint rates.
Solution: The founders conducted a full CRM cleanup, purging outdated and disengaged contacts. They leveraged engagement scoring to tailor content by buyer journey phase, significantly improving their open rates and sender score.
4. Keap (Infusionsoft) – Opt-In Gray Areas
A coaching consultancy using Keap thought that verbal consent in a webinar was enough to legally add attendees to a promotional campaign. Unfortunately, recipients didn’t expect sales emails and reported them as spam — including some who hadn’t even attended live.
Solution: The founder updated their subscriber acquisition process to include clear written opt-in confirmation. They also added a preference center so contacts could choose content frequency and categories, reducing friction and complaints.
5. GetResponse – Aggressive Retargeting
An e-commerce brand using GetResponse combined CRM data with site behavior to dynamically generate follow-up emails. One misconfiguration sent cart abandonment reminders every 4 hours for three days — a strategy that crossed the line with ISPs.
Solution: They restructured automation limits, added suppression logic, and introduced frequency caps. More importantly, they ran mailbox placement tests and authentication audits (SPF, DKIM, DMARC) to ensure inbox deliverability after recovering.
6. Constant Contact – Old Contacts, New Problems
Reactivating a dormant contact list can be a risky play. A nonprofit using Constant Contact sent their yearly appeal to a list that hadn’t heard from them in over 24 months. The result? Dozens of bounces and enough spam reports to trigger internal compliance checks.
Solution: They launched a re-engagement campaign first, asking recipients if they still wanted to hear from the organization. The contact list was then trimmed down, and re-permissioned subscribers were nurtured gradually.
7. Moosend – Templates Triggering Spam Filters
One digital agency discovered that flashy HTML templates and specific trigger words (“free,” “guaranteed”) caused problems with Moosend’s otherwise high-performing campaigns. Spam filters flagged messages based on formatting and keyword density.
Solution: The team rewrote emails in plain-text style, ensuring more natural language. They also A/B tested different template versions and used spam-testing tools like Mail-Tester before each send.
8. Sendinblue – Shared IP Headaches
Unlike some other platforms, Sendinblue relies heavily on shared IP addresses. A digital course creator noticed their open rates plummeted despite excellent engagement — later learning that one of the IPs was on a temporary block list due to abuse by another sender.
Solution: The founder upgraded to a dedicated IP address and began following gradual warming protocols. Additionally, they implemented list segmentation and removed non-engagers every 90 days to keep performance high.
9. Klaviyo – Segment Overlapping Chaos
With Klaviyo’s powerful segmentation tools, an ambitious DTC fashion brand created dozens of overlapping segments. Many customers ended up getting nearly-identical promotional emails from multiple flows — leading to confusion and higher complaint rates.
Solution: Their marketing team imposed strict rules on how segments were defined and prioritized. They also enabled frequency governance inside Klaviyo to cap total sends per subscriber per week, significantly reducing customer fatigue.
How Founders Reclaimed Reputation and Deliverability
Fixing email reputation wasn’t easy for any of these companies. Their journeys involved technical tweaks, smarter policies, and a renewed focus on deliverability fundamentals. Here are the three most common strategies that proved effective across the board:
- Authentication and Technical Audits: Most upgraded their SPF, DKIM, and DMARC records to properly align sender domains and prevent spoofing.
- Better List Hygiene: Removing cold leads, validating emails, and maintaining opt-in integrity became non-negotiable habits.
- Strategic Warming: Slowly reintroducing email campaigns with lower frequency and higher content value helped rebuild trust with ISPs.
The Role of ESP Support Teams
Several founders mentioned that the support teams at their Email Service Providers were instrumental in guiding them through these crises. Internal compliance departments shared specific headings, bounce data, and even spam trap involvement when possible.
Pro tip: If you find yourself in hot water, escalate the issue to the ESP’s deliverability or compliance team. They’re the closest thing to a map when navigating sender reputation recovery.
Preventing Spam Filter Triggers in the Future
Following recovery, each founder implemented lasting changes to prevent repeat mistakes. Best practices adopted included:
- Quarterly list audits and pruning
- Dedicated testing accounts to monitor inbox placement
- Internal deliverability diagnostics before major launches
- Rewriting nurture sequences with user personalization over automation brute force
Many teams even added “email hygiene” key performance indicators (KPIs) to their internal dashboards, tracking bounce rates, list decay, and spam complaints as seriously as they would conversions or CTRs.
Conclusion: Damage Control Is Possible
Though ending up on a blacklist or triggering spam filters is a painful journey, it’s not the end — as these nine companies prove. By identifying the root of the issue and investing in long-term fixes, they not only restored their reputation but often came back stronger than before.
In today’s email landscape, deliverability isn’t just about the tool you use — it’s about the practices you adopt. Be cautious, be compliant, and be consistent.