Testing mailflow from an on-prem Exchange Server out to O365. The mail queue on-prem is stuck due to a DNS lookup error. It is looking up the cloud mailbox and sending email to <customer_domain>.mail.onmicrosoft.com. If I try an nslookup on the specific domain it fails. If I try another customer's domain it works. At which point is the DNS lookup failing and why isn't the domain found? Shouldn't this have been automatic?
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