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Microsoft Resolves Email Misrouting Exposing User Credentials

1/26/2026

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Summary

Story summary

Microsoft fixed a misconfiguration that caused traffic intended for example.com to route to sei.co.jp subdomains via its autodiscover service.
The misrouting directed email traffic to imapgms.jnet.sei.co.jp and smtpgms.jnet.sei.co.jp, potentially exposing credentials during Outlook setup on example.com.
Cybersecurity expert Michael Taggart warned that Outlook users on example.com could have sent credentials to those subdomains.
By Monday morning, Microsoft had resolved the routing issue and had not provided an explanation.

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Story summary

Microsoft fixed a misconfiguration that caused traffic intended for example.com to route to sei.co.jp subdomains via its autodiscover service.
The misrouting directed email traffic to imapgms.jnet.sei.co.jp and smtpgms.jnet.sei.co.jp, potentially exposing credentials during Outlook setup on example.com.
Cybersecurity expert Michael Taggart warned that Outlook users on example.com could have sent credentials to those subdomains.
By Monday morning, Microsoft had resolved the routing issue and had not provided an explanation.