Such addresses are supported by Google and Microsoft products, and promoted by some governments.
RFC 3864 describes registration procedures for message header fields at the IANA; it provides for permanent and provisional field names, including also fields defined for MIME, netnews, and HTTP, and referencing relevant RFCs.
Email operates across computer networks, which today is primarily the Internet.
Some early email systems required the author and the recipient to both be online at the same time, in common with instant messaging.
Field names and values are restricted to 7-bit ASCII characters.However, once the final restrictions on carrying commercial traffic over the Internet ended in 1995, Many MTAs used to accept messages for any recipient on the Internet and do their best to deliver them. This was very important in the early days of the Internet when network connections were unreliable.and many MTAs do not accept messages from open mail relays.Neither the users nor their computers are required to be online simultaneously; they need to connect only briefly, typically to a mail server or a webmail interface, for as long as it takes to send or receive messages.Originally an ASCII text-only communications medium, Internet email was extended by Multipurpose Internet Mail Extensions (MIME) to carry text in other character sets and multimedia content attachments.