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In March 2025, one of our clients faced a serious email deliverability issue: Microsoft domains were outright blocking or filtering emails—resulting in zero inbox delivery. At the same time, other domains showed troubling engagement trends and rising bounce rates. It was a red flag for a sender reputation problem that demanded swift and strategic action.
Diagnosing the Problem
The root causes became clear:
- Older or outdated email lists were leading to high bounce rates.
- Many low-quality or fake emails had likely been submitted to access gated content.
- Microsoft domains, in particular, had responded by filtering or blocking traffic entirely.
Building a Smarter Sending Strategy
To recover, we immediately launched a multi-step email hygiene and volume control plan:
- Email Volume Planning: We aligned send volumes with inbox provider tolerances to gradually rebuild sender reputation.
- ZeroBounce Implementation: We ran all sends through ZeroBounce to pre-filter any email addresses likely to bounce.
- Global Engagement Suppression: We suppressed anyone who hadn’t opened the last six emails in the past six months.
- Exit Criteria Enforcement: We ensured “Do Not Send” contacts and converted leads were fully excluded from future sends.
Results: A Clear Turnaround
Our phased approach delivered meaningful improvements.
Campaign Specific Emails (March 16–30 vs. March 1–15):
- 66,060 sends (-8.19%)
- 0.94% bounce rate (-40.11%)
- 31.82% open rate (+4.66%)
All Campaigns & Journeys (March 30–April 12 vs. March 15–29):
- 61,825 sends (-38.49%)
- 0.99% bounce rate (-25.76%)
- 38.35% open rate (+23.15%)
By prioritizing quality over quantity, we helped our client rebuild trust with inbox providers, recover their reputation, and drive stronger engagement across the board.
With enterprise-level expertise in CRM and loyalty marketing strategy and communications, working with Response Labs puts your business in the best hands possible. Reach out and let’s talk about how we can help you.
