HOME

TheInfoList



OR:

Email forwarding generically refers to the operation of re-sending an email message delivered to one
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 Engineer ...
to one or more different email addresses. The term ''forwarding'', used for mail since long before electronic communications, has no specific technical meaning,In section 3.9.2 ''List'' of RFC 5321, the term ''forwarding'' is used ambiguously. It notes that "''the key difference between handling aliases (Section 3.9.1) and forwarding (this subsection) is the change to the 'Return-Path'' header'." That wording, new w.r.t. RFC 2821, could be interpreted as the definition of ''forwarding'', if the same term weren't used at the beginning of the same subsection with the opposite meaning. As a contributor to RFC 5321 agreed, but it implies that the email has been moved "forward" to a new destination. Email forwarding can also redirect mail going to a certain address and send it to one or more other addresses. Vice versa, email items going to several different addresses can converge via forwarding to end up in a single address in-box. Email users and administrators of email systems use the same term when speaking of both server-based and client-based forwarding.


Server-based forwarding

The
domain name A domain name is a string that identifies a realm of administrative autonomy, authority or control within the Internet. Domain names are often used to identify services provided through the Internet, such as websites, email services and more. As ...
(the part appearing to the right of ''@'' in an
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 Engineer ...
) defines the target server(s) for the corresponding class of addresses. A domain may also define backup servers; they have no mailboxes and ''forward'' messages without changing any part of their envelopes. By contrast, ''primary servers'' can deliver a message to a user's mailbox and/or ''forward'' it by changing some envelope addresses. ~/.forward files (see
below Below may refer to: *Earth * Ground (disambiguation) *Soil *Floor * Bottom (disambiguation) *Less than *Temperatures below freezing *Hell or underworld People with the surname *Ernst von Below (1863–1955), German World War I general *Fred Below ...
) provide a typical example of server-based forwarding to different recipients. Email administrators sometimes use the term redirection as a synonym for server-based email-forwarding to different recipients. Protocol engineers sometimes use the term Mediator to refer to a forwarding server. Because of
spam Spam may refer to: * Spam (food), a canned pork meat product * Spamming, unsolicited or undesired electronic messages ** Email spam, unsolicited, undesired, or illegal email messages ** Messaging spam, spam targeting users of instant messaging ...
, it is becoming increasingly difficult to reliably forward mail across different domains, and some recommend avoiding it if at all possible.


Uses of server-based forwarding to different recipients

; Role-addresses: ''info'', ''sales'', ''postmaster'', and similar names can appear to the left of ''@'' in email addresses. An organization may forward messages intended for a given role to the address of the person(s) currently functioning in that role or office. ; Pseudonym-addresses: Most domain name hosting facilities provide facilities to forward mail to another email address such as a mailbox at the user's
Internet Service Provider An Internet service provider (ISP) is an organization that provides services for accessing, using, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non-profit, or otherwise priva ...
; there are also separate providers of mail forwarding services. This allows users to have an email address that does not change if they change mailbox provider. ; Multiple, or discontinued addresses: When users change their email address, or have several addresses, the user or an administrator may set up forwarding from these addresses, if still valid, to a single current one, in order to avoid losing messages.


Forwarding versus remailing

Plain message-forwarding changes the envelope recipient(s) and leaves the envelope sender field untouched. The "envelope sender" field does not equate to the ''From'' header which Email client software usually displays: it represents a field used in the early stages of the
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 ty ...
protocol, and subsequently saved as the ''Return-Path'' header. This field holds the address to which mail-systems must send
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 "bou ...
s — reporting delivery-failure (or success) — if any. By contrast, the terms ''remailing'' or ''redistribution'' can sometimes mean re-sending the message and also rewriting the "envelope sender" field.
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. The term is often extended to include the people subscribed to such a list, so the group of subscribers is re ...
s furnish a typical example. Authors submit messages to a ''reflector'' that performs remailing to each list address. That way,
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 "bou ...
s (which report a failure delivering a message to any list- subscriber) will not reach the author of a message. However, annoying misconfigured ''vacation'' autoreplies do reach authors. Typically, plain message-forwarding does alias-expansion, while proper message-forwarding, also named ''forwarding'' tout-court serves for mailing-lists. When additional modifications to the message are carried out, so as to rather resemble the action of a
Mail User Agent The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal syst ...
submitting a new message, the term ''forwarding'' becomes deceptive and remailing seems more appropriate. In the Sender Policy Framework (SPF), the domain-name in the envelope sender remains subject to policy restrictions. Therefore, SPF generally disallows plain message-forwarding. ''Intra domain'' redirection complies with SPF as long as the relevant servers share a consistent configuration. Mail servers that practice ''inter-domain'' message-forwarding may break SPF even if they do not implement SPF themselves, i.e. they neither apply SPF checks nor publish SPF records. Consider the following forward path: :\mathit Domain ''B'' must not plainly forward a message from domain ''A'' to domain ''C'', unless it controls either the policy of ''A'' or the filtering of ''C''. Indeed, if ''A'' publishes an SPF policy that prevents ''B'' from using ''As name, and ''C'' applies sender's policy-checking, ''C'' may refuse the message according to RFC 7208. In other words, one cannot formally distinguish plain message-forwarding from illegal domain-name abuse. Sender Rewriting Scheme provides for a generic forwarding mechanism compatible with SPF.


Client-based forwarding


Automated client-based forwarding

Client forwarding can take place automatically using a non-interactive client such as a
mail retrieval agent A mail retrieval agent (MRA) is a computer application that retrieves or fetches e-mail from a remote mail server and works with a mail delivery agent to deliver mail to a local or remote email mailbox. MRAs may be external applications by themsel ...
. Although the retrieval agent uses a client protocol, this forwarding resembles ''server forwarding'' in that it keeps the same message-identity. Concerns about the envelope-sender apply.


Manual client-based forwarding

An
end-user In product development, an end user (sometimes end-user) is a person who ultimately uses or is intended to ultimately use a product. The end user stands in contrast to users who support or maintain the product, such as sysops, system administrato ...
can ''manually'' forward a message using an
email client An email client, email reader or, more formally, message user agent (MUA) or mail user agent is a computer program used to access and manage a user's email. A web application which provides message management, composition, and reception functio ...
. Forwarding ''inline'' quotes the message below the main text of the new message, and usually preserves original attachments as well as a choice of selected headers (e.g. the original ''From'' and ''Reply-To''.) The recipient of a message forwarded this way may still be able to reply to the original message; the ability to do so depends on the presence of original headers and may imply manually copying and pasting the relevant destination addresses. Forwarding ''as attachment'' prepares a
MIME Multipurpose Internet Mail Extensions (MIME) is an Internet standard that extends the format of email messages to support text in character sets other than ASCII, as well as attachments of audio, video, images, and application programs. Message ...
attachment (of type ''message/rfc822'') that contains the full original message, including all headers and any attachment. Note that including all the headers discloses much information about the message, such as the servers that transmitted it and any client-tag added on the mailbox. The recipient of a message forwarded this way may be able to open the attached message and reply to it seamlessly. This kind of forwarding actually constitutes a ''remailing'' from the points of view of the envelope-sender and of the recipient(s). The message identity also changes.


Historical development of email forwarding

RFC 821, ''Simple Mail Transfer Protocol'', by Jonathan B. Postel in 1982, provided for a ''forward-path'' for each recipient, in the form of, for example, @USC-ISIE.ARPA, @USC-ISIF.ARPA: [email protected] — an optional list of hosts and a required destination-mailbox. When the list of hosts existed, it served as a source-route, indicating that each host had to relay the mail to the next host on the list. Otherwise, in the case of insufficient destination-information but where the server knew the correct destination, it could take the responsibility to deliver the message by responding as follows: S: RCPT TO: R: 251 User not local; will forward to The concept at that time envisaged the elements of the ''forward-path'' (source route) moving to the ''return-path'' (envelope sender) as a message got relayed from one SMTP server to another. Even if the system discouraged the use of source-routing, dynamically building the ''return-path'' implied that the "envelope sender" information could not remain in its original form during forwarding. Thus RFC 821 did not originally allow plain message-forwarding. The introduction of the MX record made source-routing unnecessary. In 1989, RFC 1123 recommended accepting source-routing only for backward-compatibility. At that point, plain message forwarding became the recommended action for alias-expansion. In 2008, RFC 5321 still mentions that "systems ''may'' remove the return path and rebuild '' t' as needed", taking into consideration that not doing so might inadvertently disclose sensitive information. Actually, plain message-forwarding can be conveniently used for alias expansion within the same server or a set of coordinated servers.


~/.forward files

The reference
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 ty ...
implementation in the early 1980s was
sendmail Sendmail is a general purpose internetwork email routing facility that supports many kinds of mail-transfer and delivery methods, including the Simple Mail Transfer Protocol (SMTP) used for email transport over the Internet. A descendant of the ...
, which provided for ~/.forward files, which can store the target email-addresses for given users. This kind of server-based forwarding is sometimes called ''dot-forwarding''. One can configure some email-program filters to automatically perform forwarding or replying actions immediately after receiving. Forward files can also contain
shell script A shell script is a computer program designed to be run by a Unix shell, a command-line interpreter. The various dialects of shell scripts are considered to be scripting languages. Typical operations performed by shell scripts include file man ...
s, which have become a source of many security problems. Formerly only trusted users could utilize the command-line switch for setting the envelope sender, -f ''arg''; some systems disabled this feature for security reasons. Email predates the formalization of client–server architectures in the 1990s.The book dates in tp://ftp.uu.net/usenet/news.answers/client-server-faq.Z client-server-faqrange from the early 1990s. Although
remote procedure call In distributed computing, a remote procedure call (RPC) is when a computer program causes a procedure ( subroutine) to execute in a different address space (commonly on another computer on a shared network), which is coded as if it were a normal ...
s originated in the 1970s, they did not become widely used until networks became quite common.
Therefore, the distinction between
client Client(s) or The Client may refer to: * Client (business) * Client (computing), hardware or software that accesses a remote service on another computer * Customer or client, a recipient of goods or services in return for monetary or other valuabl ...
and
server Server may refer to: Computing *Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients Role * Waiting staff, those who work at a restaurant or a bar attending customers and su ...
seems necessarily forced. The original distinction contrasted daemons and user-controlled
programs Program, programme, programmer, or programming may refer to: Business and management * Program management, the process of managing several related projects * Time management * Program, a part of planning Arts and entertainment Audio * Progra ...
which run on the same machine. The sendmail daemon used to run with
root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the su ...
privileges so it could impersonate any user whose mail it had to manage. On the other hand, users can access their own individual mail-files and configuration files, including ~/.forward. Client programs may assist in editing the server configuration-files of a given user, thereby causing some confusion as to what role each program plays.


Virtual users

The term "virtual users" refers to email users who never log on a mail-server system and only access their mailboxes using remote clients. A mail-server program may work for both virtual and regular users, or it may require minor modifications to take advantage of the fact that virtual users frequently share the same system ''id''. The latter circumstance allows the server program to implement some features more easily, as it does not have to obey system-access restrictions. The same principles of operations apply. However, virtual users have more difficulty in accessing their configuration files, for good or ill.


Commercial products facilitating mail forward

* https://mail.getmx.com * https://www.mutantmail.com * https://forwardemail.net * https://emailforward.mx * https://improvmx.com * https://grouplist.io/ * http://forwardmx.io/ * https://bump.email/


See also

*
Chain email A chain letter is a message that attempts to convince the recipient to make a number of copies and pass them on to a certain number of recipients. The "chain" is an exponentially growing pyramid (a tree graph) that cannot be sustained indefini ...
*
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. The term is often extended to include the people subscribed to such a list, so the group of subscribers is re ...
*
Email alias An email alias is simply a forwarding email address. The term ''alias expansion'' is sometimes used to indicate a specific mode of email forwarding, thereby implying a more generic meaning of the term ''email alias'' as an address that is forwarded ...
* Email Letter * Email subject abbreviations *
Email spam Email spam, also referred to as junk email, spam mail, or simply spam, is unsolicited messages sent in bulk by email (spamming). The name comes from a Monty Python sketch in which the name of the canned pork product Spam is ubiquitous, unavoida ...
*
Mail user agent The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal syst ...
(MUA) a.k.a. email client * Message transfer agent (MTA) * Email storm * Sender Rewriting Scheme


Notes

{{DEFAULTSORT:Email Forwarding Forwarding