Email address

An e -mail address is the unique sender and recipient addresses in e- mail traffic.

An e -mail address as it is used for transport via SMTP on the Internet, consists of two parts that are separated by an @ sign:

  • The local part, called its local-part, stands in front of the @ sign.
  • The global part, called its domain-part, comes after the @ sign.

In the e- mail address [email protected] email is the local part and is the global part. Other transport mechanisms such as UUCP or X.400, use a different address syntax.

  • 4.1 Network operation
  • 4.2 Server services
  • 4.3 commerce
  • 6.1 documents
  • 6.2 External links
  • 6.3 See also

The local section ( LocalPart )

As a local section (English localpart ) the part of an e -mail address is designated, the uniquely identifies the address within the domain of the e- mail provider. Typically, the local part corresponds to the user name ( often a pseudonym) of the owner of the e- mail account. An exception to this rule, for example, alias addresses is (see e- mail account ). For e- mail distribution and mailing lists of the local section is not related to a single person.

The local part must be a respect "domain" unique string. This string must RFC 5322 contain only letters, numbers, and certain other characters: A- Za -z0 -9 # $% & ' * - / = ^ _ `{| } ~. ?. The entire local part (or bordered by points section of the local section ) can be enclosed in double quotes ( eg " JohnDoe " @ or Max "model boy ". [email protected] ). Allowed within these quotes - in addition to the characters already mentioned - even spaces and the characters " (), :; <> @ [\ ] (ASCII: 32, 34, 40, 41, 44, 58, 59, 60, 62, 64, 91-93 ) can be used (example:. . " Joe Bloggs " @ ) The character \ (backslash) and " ( quotation marks ) would have it, however, by a backslash " masked ". In addition, can be inserted within parentheses comments. This is, however, allowed only at the beginning and at the end of the local part. (Example: MaxMuster (comment) @ or (comment) [email protected] ). All characters above the ASCII code 127, including umlauts were until recently banned. Since RFC6531, which was opened in 2012, however, many Unicode characters ( international characters in many countries ) are allowed. At the beginning and end of the string there is no point may be located.

Uppercase and lowercase letters

Whether a distinction is made in the local part of an e -mail address is case- sensitive, depending on the interpretation by the recipient domain. That there may be domains in which this distinction is to be found. The RFC 5322 states: The local-part portion is a domain dependent string However, since the resulting confusion and the problems are too big, there is hardly a provider who actually between [email protected] and [email protected] differs. But must, as this possibility exists, different programs or servers that implement the SMTP protocol according to RFC 5321 is case- sensitive.

It should also be considered when choosing a personal e -mail address, uppercase letters that some of the previously mentioned web forms used in an e- mail address - possibly unnoticed - convert to lowercase. This also affects the input systems from vendors ready their equipment for the e -mail traffic of e- mail users who do not have even such devices ( e- mail account provider).

The domain part ( domain part)

The domain part which is behind the @ sign and the apply the syntax rules of the domain name system, consisting of at least three parts: a host name ( such as a company name ), a dot and a top -level domain ( an often country code or as in the example, " com" ).

Although there are very few host names that consist only of a single character (single letter second-level domain), but no top -level domains that have less than two alphabetic characters (ISO 3166-1 alpha -2 - two -letter country codes, ISO -3166 -1 Kodierliste ).

@, invalid wä[email protected] Thus, there is the possibility of regular expressions to distinguish an e -mail address from other text, although it also contains an @ sign, but again is no e- mail address.

With the introduction of the International Domain Name (IDN ) domain names may also 92 special characters outside of the pure ASCII codes, for example, contain German umlauts. This IDN to the E- mail program, however, by means of a Punycode provision in an ACE string ( ASCII Compatible Encoding) to be translated. From miller is such as xn - mller - kva. From a technical point of view changes in e -mail traffic by IDN nothing: all characters above ASCII code 127, including umlauts, remain in an e -mail address are illegal and must be encoded. Since not all email programs could automatically encode and decode punycode, one should check before use that all communication partners cope with the umlaut domains or whether you want to accept the resulting problems in purchasing.

Will exemplary addresses are required eg for manuals, so this must be one of the domains, or be used, since these domains are reserved as only by IANA for this purpose. Alternatively you can on any name the TLD. Example append (see RFC 2606 ). Other domains often used as or other hand really exist and take part actually mails to.

Length of the E -mail address

In RFC 5322, there is no length limit for e- mail addresses. However, be in RFC 5321, which defines the SMTP protocol, specified the maximum length of the Local Parts 64 and the maximum length of a domain name with 255 octets ( an octet is the same as a byte on most computers ). Together with the @ sign it would result in the maximum length of an e -mail address of 320 octets. However, in RFC 5321 and the maximum length of the "Path" element is defined, which determines the elements of the "FROM " and " RCPT TO " in the envelope, and the maximum length of octets including the separators "<" and ">" is. This results in a maximum length of the E -mail address of 254 octets, including the "@". A longer address via RFC -compliant SMTP server does not send e-mails or received.

Role accounts

Important local- Parts for E -mail addresses are described in RFC 2142 Role accounts. Role- Account is a borrowed from the English name for a task- or function- bound e- mail address. In contrast to person-related e- mail addresses the sender communicates with a role- account an ever constant contact available, regardless of holidays, illness, work or change of job a person. Role accounts are often routed through e -mail distribution to one or more persons.

The Role accounts are:


  • Abuse for abuse messages such as sending spam or DOS attacks
  • NOC to achieve the operator of the network infrastructure,
  • Security for security messages or inquiries

Server services

  • Postmaster for problems relating to the mail receipt or shipment
  • Hostmaster at name server problems
  • Webmaster for the operator of a website to contact (www is an alias )
  • Usenet for the caregiver of a news server (news is an alias, newsmaster is also common )
  • Ftp problems with the FTP server
  • Uucp for the protocol UUCP ( now rarely use)


  • Info as a general point of
  • Marketing for the appropriate department
  • Sales for sales and product information
  • Support for customer service

Historical X.400 addresses

X.400 is a 1984 established international standard that describes an alternative system of electronic messaging based on the Osi model. X.400 addresses were extremely flexible and versatile. So could the order of all parameters, such as name (S =) and first name (G =), business change (O =) and Country (C =) arbitrarily. So all the parameters had to be identified individually; the address was a mile long. Example " G = Peter; S = Zapfl; C = En; O = Deutsche Telekom; A = DBP « equal » S = Zapfl; G = Peter; C = En; O = Deutsche Telekom; A = DBP "for" Peter.Zapfl @ Telekom.DBP.De ". You have not prevailed.