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‘550 5.1.1 RESOLVER.ADR.ExRecipNotFound’ when sending email using Outlook in Office 365

Outlook

Having recently carried out a migration from an on-premise Microsoft Exchange solution to Microsoft Office 365 we have had users receiving ‘550 5.1.1 RESOLVER.ADR.ExRecipNotFound’ non-delivery reports (NDRs). Users had all their email exported to PST files and then re-imported back… Continue Reading