Some messages from a specific domain are never received by our Exchange 2010 server. No NDR on sending server.
The issue appears to be completely intermittent. Some emails get through, some dont. The disappearing messages contain attachments at times, and no attachment other times. It appears that 'most of the time' the messages ARE received. The fact that no NDR is received by sender makes it impossible for either party to know the email didn't go through. This is causing a huge communication bottleneck during important projects.
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