E-mail addresses

An email address identifies an email box to which email messages are delivered. A wide variety of formats were used in early email systems, but only a single format is used today, following the standards developed for Internet mail systems since the 1980s. This article uses the term email address to refer to the addr-spec defined in RFC 5322, not to the address that is commonly used; the difference is that an address may contain a display name, a comment, or both.

An email address such as John.Smith@example.com is made up of a local-part, an @ symbol, then a case-insensitive domain. Although the standard specifies the local part to be case-sensitive, in practice the mail system at example.com may treat John.Smith as equivalent to JohnSmith or even as johnsmith, and mail systems often limit their users' choice of name to a subset of the technically valid characters. In some cases they also limit which addresses it is possible to send mail to.

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

The transmission of electronic mail within the Internet uses the (SMTP), defined in Internet standards RFC 5321 and RFC 5322, and extensions like RFC 6531. The mailboxes may be accessed and managed by users with the (POP) or the (IMAP) with email client software that runs on a personal computer, mobile device, or with webmail systems that render the messages on a screen or on paper printouts.

The general format of an email address is local-part@domain, and a specific example is jsmith@example.com. An address consists of two parts. The part before the @ symbol (local-part) identifies the name of a mailbox. This is often the username of the recipient, e.g., jsmith. The part after the @ symbol (domain) is a domain name that represents the administrative realm for the mail box, e.g., a company's domain name, example.com.

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