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Open relay

Open relay

Open relay definition

An open relay allows any sender to transmit email through a mail server without requiring authentication. Spammers can exploit this configuration to distribute unsolicited messages. Such a setup poses a significant security risk. To prevent misuse, experts advise configuring servers to mandate user verification before allowing email transmission.

See also: relay server

Use cases of open relay

  • Internal communication. Within a private network, an open relay can facilitate unrestricted email communication between devices or departments, eliminating the need for user verification.
  • Legacy systems integration. In older infrastructures where systems might not support modern authentication methods, an open relay provides a way to integrate these systems for email communication.
  • Testing environments. Developers and IT professionals might employ open relays in controlled testing environments to simulate email flows and troubleshoot potential issues without authentication barriers.
  • Temporary connectivity. In scenarios requiring immediate, short-term email capability, like during certain migrations or setups, an open relay can offer a quick solution before more secure configurations are implemented.
  • Specialized application messaging. Certain applications might need to send notifications or alerts via email without the ability to authenticate. In these cases, an open relay can be the conduit for such communications.

Further reading

Ultimate digital security