E-Mail Loop
Encyclopedia
An email loop is an infinite loop
phenomenon, resulting from mail servers, scripts
, 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. 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.
Infinite loop
An infinite loop is a sequence of instructions in a computer program which loops endlessly, either due to the loop having no terminating condition, having one that can never be met, or one that causes the loop to start over...
phenomenon, resulting from mail servers, scripts
Scripting language
A scripting language, script language, or extension language is a programming language that allows control of one or more applications. "Scripts" are distinct from the core code of the application, as they are usually written in a different language and are often created or at least modified by the...
, 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. 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
- BandwidthBandwidth (computing)In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
: Email loops use up limited bandwidth over networks. - ProcessingData processingComputer data processing is any process that a computer program does to enter data and summarise, analyse or otherwise convert data into usable information. The process may be automated and run on a computer. It involves recording, analysing, sorting, summarising, calculating, disseminating and...
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 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 their mailbox.
Causes
- AutoresponderAutoresponderAn 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 address. These create bounce messages such as "your...
s, such as automatic "on vacation" replies - Email bouncesBounce messageIn the Internet's standard e-mail protocol SMTP, a bounce message, also called a Non-Delivery Report/Receipt , a Delivery Status Notification message, a Non-Delivery Notification or simply a bounce, is an automated electronic mail message from a mail system informing the sender of another...
due to, for example, exceeding the inbox disk quotaDisk quotaA 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:... - 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.