Which of the following identifies open ports necessary for secure email transmission?

The correct choice identifies TCP 993 and TCP 995 as the open ports necessary for secure email transmission. TCP 993 is designated for IMAPS (Internet Message Access Protocol Secure), which is the secure version of the standard IMAP protocol. This protocol is used for retrieving and managing email securely over SSL/TLS. Similarly, TCP 995 is assigned to POP3S (Post Office Protocol 3 Secure), which is the secure version of POP3 used for fetching emails, also over SSL/TLS.

Both of these ports facilitate encrypted communications, ensuring the confidentiality and integrity of email data during transmission. This is essential in today’s digital environment, where sensitive information is often transmitted via email.

The other options include ports associated with different protocols or unsecure communications. For example, TCP 25 and TCP 110 pertain to SMTP (Simple Mail Transfer Protocol) and POP3 without encryption, which do not provide the secure transmission required. Similarly, UDP 53 is related to DNS, and UDP 67 is used for DHCP, neither of which directly applies to email transmission. Lastly, TCP 143 is associated with IMAP without encryption, and TCP 161 is for SNMP, which are not relevant for secure email communication.