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@example.com. It should be read as "jsmith at example dot com". 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.
The domain name is often that of the e-mail service, such as Microsoft's Hotmail or Google's Gmail. The domain name could also be the domain name of the company that the recipient represents or even the domain of the recipient's personal site.
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 This latter was in wide use for several years, but was superseded by the generally more convenient SMTP form.
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.
To indicate where the email should go, a user normally types the "display name" of the recipient followed by the address specification surrounded by angled brackets, for example "John Smith <ap118@ficticiousdomain.ext>".
Contents
- 1 Limitations
- 2 plus addressing
- 3 Unconventional email addresses
- 4 See also
- 5 References
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Limitations
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.
As defined in RFC 2821, the local-part of an e-mail address allows up to 64 characters maximum and the domain name a maximum of 255 characters. The local-part, "MUST BE treated as case sensitive."
According to RFC 2822, the local-part of the email may use any of these ASCII characters:
- Uppercase and lowercase letters
- The digits 0 through 9
- The characters "!", "#", "$", "%", "&", "'", "*", "+", "-", "/", "=", "?", "^", "_", "`", "{", "|", "}", "~"
- The character "." provided that it is not the first or last character in the local-part.
The domain name is much more restricted. The domain name is limited to "letters, digits, and hyphens drawn from the ASCII character set ... Mailbox domains are not case sensitive." (RFC 2821). (Domain names also contain the character ".").
plus addressing
According to RFC 2821, "the local-part MUST be interpreted and assigned semantics only by the host specified in the domain part of the address. ... In particular, for some hosts the user "smith" is different from the user "Smith".
Some systems violate RFC 2822 by refusing to send mail addressed to a user on another system merely because the local-part of the address contains the plus sign (+).
There are 2 very common types of valid addresses that (as allowed by RFC 2822) contain the plus sign:
- Users who modify their email address using the "plus addressing" technique for stopping e-mail abuse. [1]. This only works when that user's mailbox is on a system, such as Gmail or Sendmail, that interpret a local-part containing the plus sign as a user specified by the part before the plus sign.
- Users who use RFC 1642 to represent Unicode characters in their user name. This only works when that user's mailbox is on a system that supports Unicode user names.
Unconventional email addresses
A new breed of email addresses have come into existence, email hacks. They are closely related to domain hacks. They make use of the commercial at symbol, @, as the letter 'a' in the creation of the email address title. Non working example email hacks that spells 'James' are 'j@m.es' and 'j@mes.com.'. Don't mistake with addresses like kkk@kkk.de or abc@abc.com
See also
- Stopping e-mail abuse
- email hack
References
- RFC 1642: UTF-7: A Mail-Safe Transformation Format of Unicode
- RFC 2821: Simple Mail Transfer Protocol
- RFC 2822: Internet Message Format
- Email addresses with a "+" are VALID
- Domain Hacks & Email Hacks - Email Hacks Explained
- Verify Email Address - Validate syntax and format + verifiy username and actual mailbox.da:E-mail-adresse
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