Email address

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An email[2] address, serving as a distinct marker for an individual’s electronic mail account, adheres to a specific format: local-part@domain. The local-part, not exceeding 64 octets, denotes the specific mailbox, and the domain, limited to 255 octets, points to the mail server. These email addresses are indispensable for correspondence through PCs, mobile devices, or webmail platforms, and frequently serve as user verification on websites. Yet, the correct format doesn’t necessarily confirm existence. Methods like callback verification are utilized to validate the existence of mailboxes. Emails are relayed via the Internet[3] utilizing the SMTP protocol as defined in RFC5321 and 5322, with the SMTP client employing the domain name[1] to locate the mail exchange IP address. Moreover, the IETF has made strides to internationalize email addresses, allowing non-ASCII characters. The email address’s domain must comply with stringent rules, including a character limit of 63 and the incorporation of letters, digits, and hyphens.

Terms definitions
1. domain name. Domain names are textual identifiers that signify internet resources, including computers and services. They symbolize ownership or control of a resource and offer a memorable name for these entities. The structure of a domain name consists of labels concatenated and separated by dots, arranged in a hierarchy from right to left. Each label can hold 1 to 63 octets, and the total domain name should not go beyond 253 ASCII characters. The Domain Name System (DNS) converts these domain names into IP addresses, aiding in the distribution of web traffic among various servers. Organized in a tree structure, domain names have Top-Level Domains (TLDs) like .com, .org, .net at the topmost level. The Internet Corporation for Assigned Names and Numbers (ICANN) manages the allocation of TLDs and accredits domain registrars. Domain names can also be internationalized, with numerous registries adopting the Internationalized domain name (IDNA) system approved by ICANN. The domain name sector is vulnerable to cyber threats such as spoofing, but protective measures are in place.
2. email. Email, a vital communication tool since its introduction in 1975, has become an integral part of our daily lives. This system functions over computer networks and the internet, enabling global message transmission and reception. While 'email' is the commonly accepted term in style guides, variations such as 'E-mail' are occasionally used, especially in American and British English contexts. The process of this system includes a sender composing a message via a Mail User Agent (MUA), which then sends it to the recipient's mail exchange server. The recipient's MUA subsequently retrieves the message. Thanks to the Multipurpose Internet Mail Extension (MIME), emails can now include multimedia content. For safety, email systems employ a store-and-forward model, whereby email servers receive, forward, store, and deliver messages. This method facilitates email exchanges without requiring users to be online simultaneously.
Email address (Wikipedia)

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) in the 1980s, and updated byRFC 5322 and 6854. The term email address in this article refers to just the addr-spec in Section 3.4 of RFC 5322. The RFC defines address more broadly as either a mailbox or group. A mailbox value can be either a name-addr, which contains a display-name and addr-spec, or the more common addr-spec alone.

An email address, such as, 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 treat John.Smith as equivalent to john.smith; some mail systems even treat them as equivalent to johnsmith. Mail systems often limit the users' choice of name to a subset of the technically permitted characters.

With the introduction of internationalized domain names, efforts are progressing to permit non-ASCII characters in email addresses.

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