An email address identifies an email box to which messages are delivered. While early messaging systems used a variety of formats for addressing, today, email addresses follow a set of specific rules originally standardized by the Internet Engineering Task Force (IETF). The term email address in this article refers to addr-spec, not to address or mailbox; i.e., a raw address without a display-name.
An email address, such as firstname.lastname@example.org, is made up from a local-part, the symbol @, and a domain, which may be a domain name or an IP address enclosed in brackets. Although the standard requires the local part to be case-sensitive, it also urges that receiving hosts deliver messages in a case-independent manner, e.g., that the mail system in the domain mycodetips.com treat ranjan as equivalent to ranjan; some mail systems even treat them as equivalent to ranjan.Mail systems often limit the users’ choice of name to a subset of the technically permitted characters.