If a third email server is not receiving email, which action should be taken to ensure email is processed by all servers?

Updating the MX (Mail Exchange) record in DNS is crucial when a third email server is not receiving emails. The MX record specifies the mail server responsible for receiving email on behalf of a domain. If the MX record is not configured correctly or does not point to the new server, emails sent to that domain may not be directed to the new email server, leading to delivery issues.

By updating the MX record, you inform other servers on the internet about the existence of the new email server and which server should handle incoming emails. This ensures that all servers can process emails intended for the domain correctly, allowing messages to reach the third email server as expected.

The other options, while relevant to different aspects of network functionality, do not address the specific issue of email delivery. For instance, enabling NTP (Network Time Protocol) synchronizes time between devices, which is essential for consistent operation but does not directly impact email routing. Configuring IMAP (Internet Message Access Protocol) on the new server is necessary for email retrieval but does not affect the receipt of emails. Finally, adding the DNS server option in DHCP pertains to network configuration and connectivity, which might help devices in finding DNS servers but does not resolve the email routing issue directly.