a folder which help us keep all the emails that have been sent

The outbox is the default folder where outgoing messages are stored until they are sent.

Place where the user's outbound email sits while the mail system is deciding whether to send it and, if so, to where (which will, of course, not include the destination intended by the user)

Collection station for outgoing correspondence before it's released through the gateway separating your local machine from a larger network, including the Internet.

a folder where you store mail before it about to be sent.

n. In many e-mail applications, the default mailbox where the program stores outgoing messages. See also e-mail1 (definition 1), mailbox. Compare Inbox.