In Microsoft Office 365 Dedicated/ITAR, a single user cannot receive web email through Microsoft Exchange Online (EOP) even though directory synchronization is enabled. Additionally, the sender receives a nondelivery report (NDR) that resembles one of the following:
550 5.7.12 RESOLVER.RST.SenderAuthenticated; Delivery restriction check failed as sender not authenticated
550 4.4.7 QUEUE.Expired; message expired
420 4.2.0 Recipient deferred because there is no Mdb
420 4.2.0 RESOLVER.ADR.Ambiguous; ambiguous address
This issue occurs if the following conditions are true:
The synchronized recipient object in Microsoft Azure Active Directory (Azure AD) is misconfigured.
The synchronized recipient object in Azure AD prevents mail routing from reaching the Office 365 Dedicated/ITAR environment.
To resolve this issue, escalate the case to Microsoft. You may submit a support incident online to Microsoft Online Services Support. Or, you can contact Microsoft Online Services Support by telephone.