MFA emails ADb2c not working

Check Azure portal → Service Health → Service issues first, because a sudden failure after working earlier—without a deployment or policy change—must be checked against tenant-specific incidents before changing the B2C configuration.

1. Confirm whether Microsoft has reported an incident

1. Sign in to the Azure portal using an account with access to the subscription associated with the B2C tenant.
2. Open Service Health → Service issues.
3. Filter for the affected subscription, region, and Azure Active Directory B2C / Microsoft Entra services.
4. Open any matching event and record its:
   • Tracking ID
   • Start time
   • Affected regions and services
   • Scope and latest update

Service Health shows incidents relevant to your Azure services and regions; active and resolved events remain available in Health history for 90 days.^1^

No Microsoft-wide B2C email-delivery incident is currently identified on the public Azure Status pages. Public status covers broad incidents, while subscription- or tenant-specific events may appear only in Service Health.^2^^3^

If Service Health shows a matching incident, avoid policy changes and monitor that event.

2. Determine the failure scope

Run one MFA attempt for each of these cases and record the exact UTC time:

• An existing user who received codes successfully this morning.
• A recipient on a different email domain.
• A mailbox whose quarantine and junk folder can be inspected.

Interpret the results as follows:

• Multiple unrelated domains fail: treat it as a probable service/delivery-path issue and escalate with the evidence below.
• Only one recipient domain fails: ask that domain’s mail administrator to inspect message trace, quarantine, spam rules, and Microsoft-managed sender filtering.
• The MFA page does not reach the code-entry stage: investigate the user flow or custom-policy execution rather than mail delivery.

Email MFA normally sends an OTP during sign-in and then prompts the user to enter that code.^4^

Avoid repeatedly selecting Send new code while delivery is delayed: multiple codes can arrive later and make it unclear which code remains usable. Delayed and intermittent OTP delivery has previously been reported in B2C scenarios.^5^

3. Capture diagnostic evidence

For every failed test, retain:

• UTC timestamp
• Policy/user-flow name
• Application ID or application name
• Tenant region
• Recipient domain only—not the complete email address
• Screen error text
• Correlation ID
• Whether the code-entry page appeared

For a custom policy, obtain the correlation ID by opening the B2C sign-in page source; it appears in a comment near the top. Use a new private-browser session for each reproduction because a new session generates a new correlation ID.^6^

If Application Insights is already connected to the custom policy, search by correlation ID and timestamp. Its traces show the executed user journey and exchanges with claims providers; new logs can take several minutes to appear.^6^

Also review the B2C tenant’s audit logs around the same UTC timestamps. B2C audit logs include platform activity, credential validation, and token issuance information useful for diagnosing whether the authentication flow progressed.^7^

4. Escalate if no incident is listed

Open Azure portal → Help + Support → Create a support request and include:

• “Azure AD B2C email MFA OTP delivery failure”
• First observed time, including time zone
• Whether all recipient domains are affected
• Service Health results
• Failed-request UTC timestamps and correlation IDs
• Policy/user-flow and application names
• Relevant Application Insights or audit-log extracts
• Business impact and reproduction frequency

Do not include complete email addresses, OTP values, secrets, or other confidential information. Microsoft’s support workflow specifically requests the start time, reproduction details, logs or browser traces, and a severity matching the business impact.^8^

References

1. Service issues
2. Azure status
3. Azure Status
4. Enable multifactor authentication in Azure Active Directory B2C (b2c-user-flow)
5. Users from Asia/UK region are facing issue on Azure AD B2C Login with Email + OTP flow - Microsoft Q&A
6. Troubleshoot Azure AD B2C custom policies and user flows (b2c-custom-policy)
7. Technical and feature overview of Azure Active Directory B2C
8. Create an Azure support request