Published: Monday 9th March,2026 3:08 pm AEDT | Derek Bell
A number of our clients have experienced a recent turn for the worse in their email deliverability metrics.
A deeper dive into the root cause suggests changes Microsoft has made to its email sender validation filters. Whilst the exact parameters are unclear, customers who have sent unusually high volumes of emails have been placed on block lists, impacting email delivery across all Microsoft domains (Outlook, Live, Hotmail, MSN).
The reality check: It’s probably not your tech
The issue appears to be unrelated to the Marketing Automation Platform, its deliverability configuration, or its email content. We’re working with several clients across a range of marketing automation platforms, all configured in line with best practices. We’ve recently seen significant spikes in email bounces across a number of campaigns, and in one case, a complete blocking of all Microsoft domains.
What we know
- We’ve raised the issue with the partner support teams of our key Marketing Automation providers and understand that there are no recent published changes to Microsoft’s filters.
- There is a flag about a known issue when you go to raise this with Microsoft directly, although it’s unclear whether this is the same issue.
- It’s pretty inconsistent across our clients in terms of email type, volume and response. Most of our clients have been ticking along at delivery rates of 98% plus, which have recently dropped by around 6%.
What can you do today?
There are a few steps that you can take to understand if you have been impacted, and maximise your email deliverability while this issue is hopefully resolved:
- Define your atypical: Avoid email sending spikes, especially to Microsoft domains. Keep your send volumes smooth.
- Stagger your sends: Consider breaking your sends into smaller chunks and stagger them over 3–4 days
- Reduce higher deliverability risk campaigns: Avoid sending to lower quality segments, especially across Microsoft domains to ensure you can still deliver your key messages to highly engaged contacts
- Monitor deliverability reporting: Check your bounce reports regularly and review the bounce reasons to identify “reputation-based rejection” and adapt accordingly.
How can we help?
Our certified team can help immediately with the following:
- Understanding any impact today and creating deliverability reports for ongoing monitoring
- Assistance with advanced segmentation, email throttling and cadence
- Identifying error codes and how to rectify them
- General advice to support your deliverability objectives
Finally, if you have heard or learned more about this issue or its resolution, please let us know so we can help others.
Technical design & Support services
The team at Marketing Cube holds a range of Oracle CX Marketing, Salesforce Marketing Cloud, HubSpot & Braze certifications, bringing deep skill & expertise to support your marketing team. In addition, our team will always stay well-informed about changes and enhancements, ensuring your team stays on the cutting edge of marketing automation.
Industry articles you may find helpful to understand deliverability in more detail
Understanding Email Deliverability: Key Factors & Key Issues
“Many marketers don’t give email deliverability much attention, that is, until they have a crisis on their hands that’s tanking their email marketing results…”
“Across the email marketing industry, deliverability rates average 85%, according to Validity. However, the Oracle Digital Experience Agency clients who work with our Email Deliverability Services team have an average deliverability rate of 97%. For an email marketing program that generates $10 million in revenue annually, boosting its deliverability rate from 85% to 97% can mean up to $1.4 million in additional revenue.”
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Since 2007, Marketing Cube has been a trusted partner for marketing automation clients, specialising in Eloqua. In 2018, we expanded our expertise to include services for Salesforce Marketing Cloud clients. Our team excels at implementing your chosen platform and providing comprehensive agency services.
With a track record of assisting nearly 180 customers across diverse industries and geographies, we offer traditional application support and efficient help desk services.
If you’re seeking agency services, such as strategic guidance, end-user coaching, training, campaign support, and more for Oracle CX Marketing, Salesforce Marketing Cloud or HubSpot, reach out to us today to discuss how we can best assist you.
Hero photo by Nihar Reddy Jangam on Unsplash
