Final answer:
ActiveSync is the required technology to receive push email notifications on a mobile device, as it allows for immediate synchronization of emails and other data.
Step-by-step explanation:
To receive push email notifications on a mobile device, the technology that is required is C. ActiveSync. While IMAP (Internet Message Access Protocol) and POP3 (Post Office Protocol 3) are email protocols that deal with the retrieval of email messages, they don't inherently handle push notifications. ActiveSync, on the other hand, is a protocol designed by Microsoft that provides push notification technology, enabling immediate synchronization of emails, calendars, contacts, and tasks when they arrive or happen. SMTP (Simple Mail Transfer Protocol) is not involved in the receiving process but is used for sending emails. Therefore, for real-time email notifications, ActiveSync is the necessary technology.