E-mail loop

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An e-mail loop is an infinite loop phenomenon, resulting from mail servers, scripts, or e-mail clients that generate automatic replies or responses. If one such automatic response triggers another automatic response on the other side, an e-mail loop is created. The process can continue until one mailbox is full or reaches its mail sending limit. In some cases, the e-mail loop could last an infinite duration. E-mail loops may be caused accidentally or maliciously, causing denial of service. Although rare, e-mail loops involving more than two participants can also occur.

E-mail loops are not as common today as in the past, due to changes to e-mail software, both on the client side and the server side, that prevent automatic replies to vacation responses and bounced mail responses.^{[citation needed]}

1 Costs of an e-mail loop
2 Causes
3 Prevention
4 External links

[edit] Costs of an e-mail loop

Bandwidth: E-mail loops use up limited bandwidth over networks.
Processing time: E-mail loops will take up processing time, and could slow down other processes.
Disk space: Automatic e-mails 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.

[edit] Causes

Autoresponders, such as automatic "on vacation" replies
E-mail bounces due to, for example, exceeding the inbox disk quota
Replies to indicate that that mail has been delivered
Replies to e-mail read-receipts

[edit] Prevention

The mail system should retain Headers of incoming E-mail while performing any type of auto-forwarding operation.
Auto Responder: Do not send more than 'x' replies to the same sender.