Open Relay Database

Open Relay Database (ORDB) is a non-profit-making organization, which protects a list of IP-addresses and e-mail servers from open relays of simple message transfer protocol (SMTP). These relays are misconfigured e-mail servers that are possible to be used as mediators for sending spam emails through them (and, conformably, spammers do use them).

With simple words, SMTP is detected as an open relay when neither the sender not the addressee are identified as local users and both of them are not inside the local domain.. Open relays are listed in the ORDB and the accepting mail servers use this base to detect SMTP. Basically, these relays themselves are not a problem; the thing is in spammers with their illegitimate usage of the relays.

By the way, open proxy-servers are not listed in the ORDB. There are some reasons for that. First, such lists do already exist and are used, and ORDB organization thinks that there is no sense in creating the similar one. Then, ORDB has too bounded resources and they choose the maintenance of the smooth and regular functioning of the base. And listing the open proxies would be an excessive engagement to people who host ORDB testing clients, as ORDB.org says (the official site of this database).

ORDB works in the following way. First, the sender conveys his e-mail to a SMTP-server, which delivers the mail to the addressee's mail server. Using Open Relay Data Base, the mail server checks if the indicated SMTP is an open relay or not. Then, there are two ways (depending on the result of checking). In the “positive” variant, the letter is being identified as legitimate and admitted. Or it can be blocked and not allowed to be delivered to the recipient, if the SMTP is being detected as an open relay.

It is possible to distinguish some advantages of ORDB. The first feature is that an administrator can check one of his systems to find out if he's really running an open relay, or not. And, as well, the administrator can control a previously opened relay to be closed. Then, ORDB always works regularly, though the resources of the base are limited.

But, on the other side, there is a chance to get a useful e-mail blocked, and besides, some legitimate mail servers can be listed as open relays. It can cause certain inconveniences to the ORDB users and it is an evidence of the low level of appropriate service.

The easiest way of using ORDB is making a DNS inquiry to http://relays.ordb.org when receiving a suspicious e-mail. The other ways are Postfix, Sendmail, Exim, Z-mailer, Smail, Procmail and others, which can be used by more professional users. Detailed instructions concerning using of them can be found at ORDB.org.

The idea of using Open Relay Database promises a quite high level of anti-spam protection of the user’s e-mail server, and it’s free and enough understandable. But it doesn’t secure sufficient guarantees of protection against false-positive e-mails, and it’s the quite appreciable disadvantage. Despamious fully supports Open Relay Database and uses it as one of the antispam protection milestones.