You are setting up the Symantec Data Loss Prevention Cloud Service for Email, with O365 in Reflecting mode.
But messages are being rejected with various attribution errors.
Possible errors on messages as following:
451 4.4.62 Mail sent to the wrong Office 365 region. ATTR35. For more information please go to https://go.microsoft.com/fwlink/?linkid=865268 [SN2NAM02FT002.eop-nam02.prod.protection.outlook.com]
550 5.7.64 TenantAttribution; Relay Access Denied [SN1NAM02FT001.eop-nam02.prod.protection.outlook.com]
These appear to suggest that there is an issue with DNS for your domains in O365, however, it is more likely that there is a problem with the configuration of an Inbound Connector - specifically in regard to the one configured for the DLP Cloud Service for Email.
Verify that the Inbound Connector is setup as per the existing documentation:
In particular, the "550 5.7.64 TenantAttribution; Relay Access Denied" error can indicate that:
Both of the above errors (451 and 550) have also been seen when the Inbound Connector was not configured at all.