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Exchange Outbound Email Delivery Failures - DNS Resolution Issue (Error 450 4.4.312)
Hi, Microsoft Exchange Online/Office 365 servers are failing to deliver emails to our mail server due to DNS resolution failures. This issue started approximately one week ago with no configuration ...
On the Exchange server, run Set-SendConnector DNSRoutingEnabled $true to enable DNS routing, and check that the firewall allows TCP port 53.