Tag Archives: unable to relay

Centralized Mailflow: NDR Remote Server returned ‘550 5.7.1 Unable to relay’

 Environment: Mailbox hosted on the Exchange Online Hybrid on-prem Exchange 2010/2013 with Microsoft Exchange Online Centralized Mailflow configured for Exchange 2013 Route all emails through on-premises configured for Exchange 2010 Accepted domain configured either Managed or Authoritative on the Exchange … Continue reading

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