The Lumber Cartel, local 42 (Canadian branch)
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Glossary - eMail address

An eMail address is the most common form of user identification used on the internet.  The eMail address, in its entirety, is unique, which is why it's so useful.  The vast majority of eMail addresses are operated manually by people, with the remaining addresses being handled by automated systems.

The anatomy of an eMail address can be viewed in four pieces:

  1. Display name (a.k.a., "comments")
  2. Local-part (the portion before the "@" symbol)
  3. Delimiter (the "@" symbol)
  4. Internet domain name (the portion after the "@" symbol)

When the first piece is used, a set of "angle brackets" (less-than "<" and greater-than ">" signs) that surround the eMail address (comprised of pieces 2, 3, and 4) are required; without the first piece, these angle brackets are optional.

Valid characters

There is a lot of confusion about which characters are actually permitted in an eMail address.  Many people have written about it, and unfortunately a lot of erroneous information about these details have been used in production systems.  Common erors include the exclusion of these four popular characters:  +-._

As per the relevant internet standards documents, only the following characters are permitted in a raw eMail address (this will be of particular interest to software developers who need to write code that validates eMail addresses):

Local-part (the portion before the "@" symbol)

Internet domain name (the portion after the "@" symbol)

For the internet domain name, the special characters ":[]" are used to specify domain literals, which are IP addresses used in place of internet domain names.  Most systems that are validating end-user input (e.g., submitted through web-based forms) can safely exclude these characters.


The standards that the internet is built on are defined in a series of documents (that currently number in the thousands) called RFCs (Request For Comments), and generally contain highly technical information that is, in particular, useful to developers and systems administrators.  The format of eMail addresses is defined in RFC 2822 (which obsoletes RFC 822).

See also

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