An email loop is an
infinite loop phenomenon, resulting from
mail server
Within the Internet email system, a message transfer agent (MTA), or mail transfer agent, or mail relay is software that transfers electronic mail messages from one computer to another using SMTP. The terms mail server, mail exchanger, and MX host ...
s,
scripts
Script may refer to:
Writing systems
* Script, a distinctive writing system, based on a repertoire of specific elements or symbols, or that repertoire
* Script (styles of handwriting)
** Script typeface, a typeface with characteristics of handw ...
, or
email clients that generate automatic replies or responses. If one such automatic response triggers another automatic response on the other side, an email loop is created. The process can continue until one
mailbox is full or reaches its mail sending limit. In theory, the email loop could last indefinitely. Email loops may be caused accidentally or maliciously, causing
denial of service
In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host connect ...
. Although rare, email loops involving more than two participants can also occur.
Email loops are not as common today as in the past, due to changes to email software, both on the client side and the server side, that prevent automatic replies to vacation responses and bounced mail responses.
Costs of an email loop
*
Bandwidth: Email loops use up limited bandwidth over networks.
*
Processing
Processing is a free graphical library and integrated development environment (IDE) built for the electronic arts, new media art, and visual design communities with the purpose of teaching non-programmers the fundamentals of computer programming ...
time: Email loops will take up processing time, and could slow down other processes.
*
Disk space: Automatic emails are usually stored in the mailboxes of participants.
* Human time:
Network administrators
A network administrator is a person designated in an organization whose responsibility includes maintaining computer infrastructures with emphasis on local area networks (LANs) up to wide area networks (WANs). Responsibilities may vary between org ...
may have to intervene to fix the problem, or clean up mailboxes. Also the mailbox user/owner will have to delete the numerous responses in order to clean up the mailbox.
Causes
*
Autoresponder An autoresponder is a computer program that automatically answers e-mail sent to it. They can be very simple or quite complex.
The first autoresponders were created within mail transfer agents that found they could not deliver an e-mail to a given ...
s, such as automatic "on vacation" replies
*
Email bounces due to, for example, exceeding the inbox
disk quota
A disk quota is a limit set by a system administrator that restricts certain aspects of file system usage on modern operating systems. The function of using disk quotas is to allocate limited disk space in a reasonable way.
Types of quotas
There ...
* Replies to indicate that that mail has been delivered
* Replies to
email read-receipts
* Misconfigured email servers that try to deliver messages to systems that pass the message along to another host, with a loop leading in a circle. (Modern mail systems will detect mail forwarded back and forth between two hosts, but a routing loop involving three hosts is much harder to detect.)
Prevention
* The mail system should retain headers of incoming email while performing any type of auto-forwarding operation.
* Auto Responder: Do not send more than 'x' replies to the same sender.
* Headers hinting at auto-responders, like
X-Auto-Response-Suppress: All (Microsoft Exchange) or
Auto-Submitted: auto-generated (RFC 3834
)
References
External links
Vacation E-Mail LoopThe Free Dictionary
Email
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