An open mail relay is an SMTP (email) server configured in such a way that it allows anyone on the Internet to relay (i.e. send) email through it.

History and technology

Until the 1990s this was the normal configuration for a mail server and was often the default on Unix systems at installation. This was due, in part, to the traditional method in which email (through and beyond the Internet) was passed from computer to computer via modems on telephone lines, often never touching the small Internet of the time. It was cheaper and simpler for email to be passed from computer to computer until it reached its destination than to connect directly to the target computer (e.g. via modem) and log in to transfer the mail. Filtering and speed of email delivery were not priorities. Furthermore, the small number of servers on the Internet generated a peer pressure on standards and conventions of its use. Moreover, on the government and educational servers with which the Internet was started, the transfer of commercial messages was forbidden by federal edict, as it was a government operation.

Nowadays, email transfer by "relaying," or pass-along methods, is almost forgotten. Backbone networks and Internet switches make it cost effective and expeditious for end-user PCs or even cellphones to send mail directly to the target host, without need for relaying through a "middleman" site. The underlying communication methods of the Internet already provide end-to-end connectivity via a pass-along method.

Abuse by spammers

In the mid-1990s, once the internet became more of a publicly available (and moreover, commercial) service, it wasn't long until it was utilized by mass-marketers, today known in the electronic world as spammers. As spam soon became widely unpopular, especially by email server administrators who had to deal with the increased unsolicited traffic, spammers discovered that they could minimize or avoid detection by re-routing their email through third party email servers. After this practice became widespread, the mere practice of operating an open relay email server became frowned upon among a significant number of Internet server administrators and other prominent users, many of which were veterans of the Internet's non-commercial era.

Anti-spam efforts against open relays

Many ISPs use DNSBLs (DNS-based Blocking Lists) to disallow mail from open relays. Once a mail server is detected or reported that allows third parties to send mail through them, they will be added to one or more such lists, and other email servers using those lists will reject any mail coming from those sites.

This trend reduced the percentage of mail senders that were open relays from over 90% down to well under 1% over several years. This led to spammers adopting other techiques, such as the use of open proxies to send spam. Although open relays are no longer widely used to send spam, many sites continue to refuse mail traffic from them.

One consequence of the new unacceptability of open relays was an inconvenience for some end users and certain ISPs. To allow customers to use their email addresses at Internet locations other than the company's systems (such as at school or work), many mail sites explicitly allowed open relaying so that customers could read and send email via the ISP from any location. Once open relay became unacceptable due to abuse (and unusable due to blocking of open relays) ISPs and other sites had to adopt new protocols to allow remote users to send mail. These include SMTP AUTH , POP=before-SMTP, and the use of virtual private networks (VPNs).

The Can Spam Act of 2003 makes it illegal to send spam through an open relay, but makes no provision regarding sending personal email through them or regarding their operation.

Modern-day proponents

The most famous open mail relay operating today is probably that of John Gilmore, who argues that running an open relay is a free speech issue. His server is included on many open relay blacklists (many of which are generated by "automatic detection", that is, by anti-spam blacklisters sending an (unsolicited) test email to other servers to see if they will be relayed). He has never sent any spam personally, yet these measures cause much of his outgoing email to be blocked. Along with his further deliberate configuration of the server, his open relay enables people to send email without their IP address being directly visible to the recipient and thereby send email anonymously .

Gilmore contends he has a right to configure his computer however he pleases, and others have the right to configure their computers to ignore him. However, since open-relay blacklisting is most commonly done at the ISP level, many end users have this decision made for them without their explicit request. Many ISPs have been unwilling to remove the blacklists that prevent his emails from reaching recipients on the ISP's network or implement any other method (such as a whitelist) to allow his email through. As a result, he is unable to communicate by email with many of his friends and business partners.

External links

• ORDB.org - the Open Relay Database