Fix Microsoft 365 Domain Reputation Block – Exchange Online 2026

Start by locating and submitting the blocked message through Exchange Admin Center:

1. Sign in to Exchange Admin Center at https://admin.exchange.microsoft.com
2. Navigate to Protection → Quarantine
3. Search for messages from the affected domain using the search filters
4. Click on the quarantined message to view details
5. Verify the detection technology shows Domain reputation
6. Confirm DMARC, DKIM, and SPF show as Pass
7. Click the three dots (...) menu
8. Select Submit for review
9. Ensure the email network message ID appears correctly
10. Verify the recipient email address is listed
11. Select I've confirmed it's clean
12. Click Next, then Submit

Open a Microsoft 365 support case to escalate the domain reputation issue:

1. From the Report submissions page, select your submitted message
2. Copy the Submission ID (format: similar to 3fa85f64-5717-4562-b3fc-2c963f66afa6)
3. Navigate to Microsoft 365 Admin Center at https://admin.microsoft.com
4. Go to Support → New service request
5. Select Exchange Online as the service
6. Choose Mail flow and transport as the issue type
7. In the description, include:
   • Domain name experiencing reputation block
   • Submission ID from step 2
   • Request to forward to Microsoft Defender team
   • Mention all email authentication is properly configured
8. Attach screenshots of the quarantine details and authentication status
9. Submit the support request

Analyze message patterns to provide additional evidence for your support case:

1. In Exchange Admin Center, navigate to Mail flow → Message trace
2. Set date range to last 7-10 days
3. Enter your domain in the Sender field
4. Click Search to run the trace
5. Export results by clicking Download report
6. Analyze the data for patterns:
   • Percentage of messages blocked vs delivered
   • Specific recipients or domains affected
   • Timeline of when blocking started
7. Create a summary document showing:
   • Total messages sent vs blocked
   • Authentication status for blocked messages
   • Evidence that legitimate business communication is affected
8. Attach this analysis to your support case

Use PowerShell for more detailed analysis:

Get-MessageTrace -SenderAddress "*@yourdomain.com" -StartDate (Get-Date).AddDays(-7) -EndDate (Get-Date) | Where-Object {$_.Status -eq "Failed" -or $_.Status -eq "Quarantined"} | Export-Csv -Path "C:\temp\blocked_messages.csv" -NoTypeInformation

Ensure your domain's email authentication is optimally configured while waiting for Microsoft's response:

1. Verify SPF record using PowerShell:

Resolve-DnsName -Name "yourdomain.com" -Type TXT | Where-Object {$_.Strings -like "v=spf1*"}

2. Check DKIM configuration in Exchange Admin Center:
   • Navigate to Protection → Authentication policies
   • Select your domain and verify DKIM is enabled
   • Ensure DKIM keys are published in DNS
3. Verify DMARC policy:

Resolve-DnsName -Name "_dmarc.yourdomain.com" -Type TXT

4. Test email authentication using Microsoft's tools:
   • Send test emails to Microsoft 365 accounts
   • Check message headers for authentication results
   • Verify all three protocols show 'pass' status
5. If any authentication fails, update DNS records accordingly
6. Wait 24-48 hours for DNS propagation
7. Document all authentication improvements in your support case

While waiting for Microsoft to resolve the domain block, implement these temporary measures:

1. Configure Safe Senders list for critical recipients:
   • Contact important clients/partners
   • Ask them to add your domain to their Safe Senders list
   • Provide instructions for Outlook and Outlook Web App
2. Use alternative sending methods for urgent communications:
   • Send from a different subdomain if available
   • Use a third-party email service temporarily
   • Implement direct phone/SMS notifications for critical messages
3. Monitor and document ongoing impact:
   • Track delivery failures and business impact
   • Maintain communication logs with affected parties
   • Document financial or operational losses
4. Set up proactive monitoring:

# PowerShell script to monitor message delivery
$StartDate = (Get-Date).AddHours(-1)
$EndDate = Get-Date
$FailedMessages = Get-MessageTrace -SenderAddress "*@yourdomain.com" -StartDate $StartDate -EndDate $EndDate | Where-Object {$_.Status -eq "Failed" -or $_.Status -eq "Quarantined"}
if ($FailedMessages) {
    Send-MailMessage -To "admin@yourdomain.com" -From "monitoring@yourdomain.com" -Subject "Email Delivery Issues Detected" -Body "Failed messages detected: $($FailedMessages.Count)"
}

5. Escalate through Microsoft Partner channels if available
6. Consider engaging Microsoft Premier Support for faster resolution