For questions relating to implementing email clients, or for code extending or interacting with an existing mail client.
An email client, email reader, or more formally, mail user agent (MUA) is a computer program used to manage a user's email.
The term can refer to any system capable of accessing the user's email mailbox, regardless of it being a mail user agent, a relaying server, or a human typing on a terminal. In addition, a web application that provides message management, composition, and reception functions is sometimes also considered an email client, but more commonly referred to as webmail.
Popular email clients include Microsoft Outlook, Pegasus Mail, Mozilla's Thunderbird, and Apple Inc.'s Mail.