Which protocol is used for outgoing mail?

The correct response highlights that SMTP, or Simple Mail Transfer Protocol, is specifically designed for sending emails from a client to a server or between servers. It facilitates the transfer of outbound mail, making it the backbone for email transmission on the internet. When you send an email, your email client communicates with the email server using SMTP to relay your message to the recipient's mail server.

IMAP (Internet Message Access Protocol) is primarily used for retrieving messages from a mail server. It allows users to access and manipulate their email messages as if they were stored locally, but it does not handle outgoing mail.

HTTP (Hypertext Transfer Protocol) is a protocol used for transferring web pages on the internet and is not related to email transmission at all.

FTP (File Transfer Protocol) is intended for transferring files over a network and does not pertain specifically to email functions.

Thus, when considering outgoing mail specifically, SMTP is undoubtedly the correct choice.