XCON: Routing Restrictions Do Not Work with % Addresses RFC 1123 5.2.16 (244346)

SYMPTOMS

The source routing that is specified in Request for Comments (RFC) 1123 5.2.16 allows for addresses to be encapsulated in the recipient part of a Simple Mail Transfer Protocol (SMTP) address. This enables a person to send an e-mail address to an SMTP host, and the host then parses the address and reroutes the message to the intended recipient.

An Internet Mail Service that is set up to receive only messages that are destined for the SMTP domain name processes source routing messages completely before it sends back a non-delivery report (NDR).

Messages are completely processed, even if routing restrictions are specified and a user uses the source routing that is specified in RFC 1123 5.2.16. This may be the tactic that is used for a denial of service attack on an Internet Mail Service.