MAILER-DAEMON@yahoo.com what does this stand for and is this a Yahoo company?

Software in a mail server that delivers messages to recipients. When you get a MAILER-DAEMON@whatevercompany.... message in your inbox, the server at that company is informing you that it is returning your message because of some failure. The "to" e-mail address may no longer be valid, or there may be a problem routing the message to the appropriate mail server. Your domain name may be on a blacklist, and the server is refusing all incoming messages from it. Double check the email.

daemon

Pronounced DEE-mun or DAY-mun. A process that runs in the background and performs a specified operation at predefined times or in response to certain events. The term daemon is a UNIX term, though many other operating systems provide support for daemons, though they're sometimes called other names. Windows, for example, refers to daemons as System Agents and services.
Typical daemon processes include print spoolers, e-mail handlers, and other programs that perform administrative tasks for the operating system. The term comes from Greek mythology, where daemons were guardian spirits.