Open mail relay
An open mail relay
is an SMTP
server configured in such a way that it allows anyone on the Internet
to relay email
through it. Until the 1990s
this was the normal configuration for a mail server and was often the default on Unix
systems at installation. However after spammers
started abusing open relays to forward their own messages, it became frowned upon by some members of the Internet community to run such a server. The Can Spam Act of 2003
outlaws this use in the United States
. Many ISPs
use DNSBLs to prevent open mail relay servers to send mail to them.
The most famous mail relay is probably that of John Gilmore, who argues that running an open relay is a free speech issue, and that since he has never sent any spam personally he has a right to configure his computer however he pleases.