An e-mail address identifies a location to which e-mail can be delivered. A modern Internet e-mail address (using SMTP) is a string of the form jsmith@domain.example. It should be read as "jsmith at domain dot example". The part before the @ sign is the local part of the address, often the username of the recipient, and the part after the @ sign is a domain name which can be looked up in the Domain Name System to find the mail exchange servers accepting e-mail for that address.

Earlier forms of e-mail address included the somewhat verbose notation required by X.400, and the UUCP "bang path" notation, in which the address was given in the form of a sequence of computers through which the message should be relayed. This latter was in wide use for several years, but was superceded by the generally more convenient SMTP form.

The format of Internet e-mail addresses is defined in RFC 2822, which permits only a subset of ASCII characters in e-mail addresses. RFC 1642, however, defines UTF-7, a way of encoding all Unicode characters using only characters permitted in e-mail; e-mail addresses using this standard are most commonly seen in Asia and not widely used in Europe or North America.

Addresses found in the headers of e-mail should not be considered authoritative, because SMTP has no mechanism for authentication. Forged e-mail addresses are often seen in spam and in phishing and similar scams, leading to several initiatives, such as Sender ID, which aim to make such forgeries easier to spot. The most reliable method of authentication, however, is to require that messages be digitally signed.

See also

• Stopping e-mail abuse

References

• RFC 1642: UTF-7: A Mail-Safe Transformation Format of Unicode
• RFC 2822: Internet Message Format