Push email is an email system that provides an always-on capability, in which when new email arrives at the mail delivery agent (MDA) (commonly called mail server), it is immediately, actively transferred (pushed) by the MDA to the mail user agent (MUA), also called the email client, so that the end-user can see incoming email immediately. This is in contrast with systems that check for new incoming mail every so often, on a schedule. Email clients include smartphones and, less strictly, IMAP personal computer mail applications.