When a user in a Microsoft Office 365 environment tries to send an email message, they may receive a Non-Delivery Receipt (NDR) that resembles the following: <Domain_URL> #<<Domain_URL>#5.4.6 smtp;554 5.4.6 Hop count exceeded - possible mail loop> #SMTP#
This issue may occur if the domain exists as a disabled domain in Microsoft Forefront Online Protection for Exchange (FOPE) under the BPOS account. The domain can be disabled in FOPE if the following events occurred:
To resolve this issue, use either a cmdlet in Microsoft Windows PowerShell, or contact FOPE Support.
Method 1: Use Windows Power Shell
Use the Set-AcceptedDomain cmdlet together with the OutboundOnly parameter to force FOPE to recognize the domain, and create the appropriate records. The OutboundOnly parameter specifies whether this accepted domain is an internal relay domain for the on-premises deployment for organizations that have coexistence with a cloud-based organization.
The authoritative accepted domain for the on-premises deployment is configured as an internal relay accepted domain on the cloud side. If the on-premises deployment is using Microsoft Forefront Online Protection for Exchange, you must set this parameter to $true for the accepted domain that represents your on-premises deployment. This parameter is used only if the DomainType parameter is set to Authoritative or InternalRelay. The default value is $false.
To use Windows PowerShell, follow these steps:
Set-AcceptedDomain <Domain> -OutboundOnly $true
Set-AcceptedDomain <Domain> -OutboundOnly $false
For more information about the Set-AcceptedDomain cmdlet, view the TechNet topic Set-AcceptedDomain.
Method 2: Contact FOPE Support