An email alias is a

email address An email address identifies an email box to which messages are delivered. While early messaging systems used a variety of formats for addressing, today, email addresses follow a set of specific rules originally standardized by the Internet Enginee ...

used for forwarding.

Term

The term ''alias expansion'' is sometimes used to indicate a specific mode of

email forwarding Email forwarding generically refers to the operation of re-sending a previously delivered email to an email address to one or more different email addresses. The term ''forwarding'', used for mail since long before electronic communications, has n ...

, thereby implying a more generic meaning of the term ''email alias'' as an address that is forwarded in a simplistic fashion.RFC 5321 defines ''alias'' expansion as opposed to the ''list'' expansion of mailing lists, noting that the replacement of the address to whom

bounce message A bounce message or just "bounce" is an automated message from an email system, informing the sender of a previous message that the message has not been delivered (or some other delivery problem occurred). The original message is said to have "boun ...

s are returned makes a key difference. An email alias is different from a contact group, or distribution list. According to Microsoft, a contact group is "a grouping of e-mail addresses collected under one name. A message sent to a contact group goes to all recipients listed in the group."

Usage

aliases A pseudonym (; ) or alias () is a fictitious name that a person assumes for a particular purpose, which differs from their original or true meaning (orthonym). This also differs from a new name that entirely or legally replaces an individual's ow ...

can be created on a mail server that simply forwards email messages addressed to an email alias on to another, the specified email address. An email alias may be used to create a simple replacement for a long or difficult-to-remember email address. It can also be used to create a generic email address such as webmaster@

example.com The domain names example.com, example.net, example.org, and example.edu are second-level domain names in the Domain Name System of the Internet. They are reserved by the Internet Assigned Numbers Authority (IANA) at the direction of the Inter ...

and [email protected]. On

UNIX Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

-like systems, email aliases may be placed into the file /etc/aliases and have the form: :local-alias-name: adifferentlocaluser, anotherlocaluser, [email protected]

Issues

Control

Messages forwarded through an email alias retain the original

SMTP The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients typi ...

envelope sender {{Redir, Return path, the term in electronics, Return path (electronics) A bounce address is an email address to which bounce messages are delivered. There are many variants of the name, none of them used universally, including return path, reve ...

and recipient. If the message is a blind carbon copy, the recipient can only tell whether the message was forwarded through the alias by examining the message headers. However, the standard does not mandate mentioning the envelope recipient in the headers. Therefore, recipients of a message may not be able to recover what email address has been used by the sender to eventually deliver the message to their mailbox. Recipients who cannot trace what address the sender used are unable to ask the sender to stop sending, because the sender most likely will not be able to associate their current email address with the one used for sending. Even if users are able to learn the exact address used for sending, their mail client may not provide a convenient way to submit a reply using the latter as the sender address of the response. In other words, aliasing is not reversible. This is particularly relevant in

opt-out The term opt-out refers to several methods by which individuals can avoid receiving unsolicited product or service information. This option is usually associated with direct marketing campaigns such as e-mail marketing or direct mail. A list of th ...

situations where the sender does not provide a reliable mechanism ''in the body'' of the message. Typically,

newsletter A newsletter is a printed or electronic report containing news concerning the activities of a business or an organization that is sent to its members, customers, employees or other subscribers. Newsletters generally contain one main topic of ...

s sent to ''undisclosed recipients'' can be sent submitting the body ''once'' along with a list of recipients, which is much less resource intensive than submitting a different body for each recipient. However, if VERP or BATV are being used (e.g. to prevent email backscatter), the

electronic mailing list A mailing list is a collection of names and addresses used by an individual or an organization to send material to multiple recipients. Mailing lists are often rented or sold. If rented, the renter agrees to use the mailing list only at contra ...

software will send individual messages to each recipient with a different SMTP FROM address.

Abuse

The recipient's SMTP server sees only the forwarding system's

IP address An Internet Protocol address (IP address) is a numerical label such as that is assigned to a device connected to a computer network that uses the Internet Protocol for communication. IP addresses serve two main functions: network interface i ...

. In general it has no reason to trust the Received: headerfield generated by the forwarding system and does not know the originating system's IP address. Therefore, recipients cannot reliably distinguish

spam Spam most often refers to: * Spam (food), a consumer brand product of canned processed pork of the Hormel Foods Corporation * Spamming, unsolicited or undesired electronic messages ** Email spam, unsolicited, undesired, or illegal email messages ...

''to the alias address'' from spam ''generated on the forwarding system''. When a recipient reports a message to his

ISP An Internet service provider (ISP) is an organization that provides a myriad of services related to accessing, using, managing, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non ...

as spam, the ISP credits that spam to the forwarding system. ISPs with low abuse thresholds may begin blocking email from the forwarding system.

Notes