The default email client included with macOS is Mail, also known as Apple Mail. Apple bundles it with the operating system so users can connect accounts such as iCloud, Gmail, Yahoo Mail, Outlook, and many IMAP or Exchange services without installing a separate client.
Mail has roots outside Apple’s original software. It grew from NeXTMail, an application created for NeXTSTEP, the operating system developed by NeXT. After Apple acquired NeXT in 1997, NeXTSTEP technology became the foundation of Mac OS X, and the mail application was carried forward as Mail.
Mail is more than a simple inbox viewer. It supports folders and search, junk-mail filtering, signatures, rules, multiple accounts, and integrations with other Apple services. It uses SMTP for sending and can retrieve messages through IMAP, POP3, or Exchange. Thunderbird and Outlook are popular alternatives, while Eudora is a historically important third-party client, but none is the built-in macOS default. The app’s name is simply “Mail,” even though “Apple Mail” is commonly used to distinguish it from generic email software.