To answer this question, let's go through each option to understand which protocol is not used for Incoming Mail Service:
Option A) POP3 - POP3 (Post Office Protocol version 3) is a protocol used for retrieving emails from a mail server. It is commonly used for incoming mail service.
Option B) SMTP - SMTP (Simple Mail Transfer Protocol) is a protocol used for sending emails from a mail client to a mail server. It is not used for retrieving emails, so it is not typically used for incoming mail service.
Option C) IMAP - IMAP (Internet Message Access Protocol) is a protocol used for accessing and managing emails on a mail server. It is commonly used for incoming mail service.
Option D) HTTP - HTTP (Hypertext Transfer Protocol) is a protocol used for transmitting data over the internet. It is not specifically designed for email services and is not commonly used for incoming mail service.
Based on the explanations above, the correct answer is Option B) SMTP. SMTP is not used for Incoming Mail Service.