Which of the following network protocols is used for sending outbound email from a host?

A.
SMTP

B.
POP

C.
RTP

D.
IMAP

Post Office Protocol version 3 (POP3) is a standard mail protocol used to receive emails from a remote server to a local email client. POP3 allows you to download email messages on your local computer and read them even when you are offline.
The Internet Message Access Protocol (IMAP) is a mail protocol used for accessing email on a remote web server from a local client. IMAP and POP3 are the two most commonly used Internet mail protocols for retrieving emails. Both protocols are supported by all modern email clients and web servers.
Main difference between IMAP and POP3:
The POP3 protocol assumes that there is only one client connected to the mailbox. In contrast, the IMAP protocol allows simultaneous access by multiple clients. IMAP is suitable for you if your mailbox is about to be managed by multiple users.
Simple Mail Transfer Protocol (SMTP) is the standard protocol for sending emails across the Internet. SMTP uses TCP port 25.