You have a hybrid deployment that contains a Microsoft Exchange Online tenant and an on-premises Exchange Server 2019 server named Server1.
Server1 uses a certificate from a third-party certification authority (CA). The certificate is enabled for the SMTP service.
You replace the certificate with a new certificate.
You discover that delivery fails for all email messages sent from Server1 to your Microsoft 365 tenant.
You receive the following error message for all the queued email messages: “450 4.4.101 Proxy session setup failed on Frontend with 451 4.4.0 Primary target IP address responded with 451 5.7.3 STARTTLS is required to send mail.” You need to ensure that the messages are delivered successfully from Server1 to the Microsoft 365 tenant.
What should you do?
A. From the Exchange admin center, update the certificate thumbprint in the properties of a connector
B. From Server1, regenerate the certificate and select Make private keys exportable
C. From the firewall, disable SMTP content inspection
D. From Server1, enable the new certificate for the IMAP4 service
