Microsoft 365 Messaging — Question 48

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?

Answer options

• A. From Server1, enable a self-signed certificate for the SMTP service.
• B. From Server1, enable the new certificate for the IMAP4 service.
• C. From Server1, run the iisreset command.
• D. Run the Exchange Hybrid Configuration wizard.

Correct answer: D

Explanation

The correct action is to run the Exchange Hybrid Configuration wizard (D), as it will reconfigure the hybrid setup and ensure that the new certificate is correctly applied for SMTP communications. Options A and B do not address the SMTP service directly, while option C would not resolve any certificate-related issues impacting email delivery.