Email loop

from Wikipedia, the free encyclopedia

E-mail loop is a term borrowed from English for a loop in which an e-mail is forwarded endlessly ( endless loop ).

E-mail loops occur, for example, when two e-mail addresses are forwarded to each other .


  •   - forwarded to →
  •   - forwarded to →

If an e-mail is now sent to or , an e-mail loop is created in which the e-mail is sent endlessly back and forth between the two addresses - unless further measures do so prevent.

Such e-mail loops are not limited to two addresses, but can theoretically extend over any number of forwardings. Then the loop is not obvious to any of the supervisors involved. E-mail loops are particularly problematic if one of the addresses involved is forwarded to a mailing list or an e-mail distribution list .

Detection of email loops

As a rule, e-mail loops can be recognized by a noticeable increase in e-mail traffic (volume and number) or an unusually high load on a mail server. If an e-mail distribution list is included in the e-mail loop, the recipients not involved in the endless loop usually notice the problem very quickly when they see a large number of identical e-mails arriving at short intervals.


Most mail servers have a means by which e-mail loops can be detected and broken. As a rule, an email is not forwarded if it has already been forwarded via a certain number of mail servers (recognizable by the received headers ) or if the receiving mail server recognizes that it has already delivered this mail to the same recipient.

The fact that e-mail loops still occur that are not automatically interrupted is mainly due to inadequate configurations of the mail server or to software that either does not take into account the danger of e-mail loops or does not sufficiently take into account. Affected are often autoresponder that deliver a message to the sender (eg. Absence wg. Holidays ), although the received message already own an auto-reply is (then talk to two auto-responder) or mailing lists that Received header removed automatically, thus making automatic loop detection (see above) impossible.