Let's examine the options given in the question to determine the role of the "Outbox" in an email system:

1. Option 1: It contains emails that are currently being drafted.
   This statement is incorrect. Emails that are being drafted are typically found in the "Drafts" folder, not the Outbox.
2. Option 2: It temporarily stores emails that are queued for sending.
   This is the correct option. The Outbox is designed to temporarily hold emails that have been composed and are queued for sending. These emails wait in the Outbox until they can be sent to the recipient's email server, especially when there is no immediate internet connection or if there are sending errors.
3. Option 3: It holds emails that have been successfully sent.
   After an email is successfully sent, it is usually moved to the "Sent Items" or "Sent Messages" folder, not the Outbox. Therefore, this statement is incorrect.
4. Option 4: It is used to receive incoming emails.
   This statement is also incorrect. Incoming emails are stored in the "Inbox," not the Outbox. The Outbox's function is related to outgoing emails.

Based on the above analysis, the correct answer is that the Outbox temporarily stores emails that are queued for sending.