Protect Yourself From Spam

What are DNS blacklists?/What is an open relay?

What is Spam?

• When is Spam Spam?

• Where does the term “Spam” come from?

• Why do people send Spam?

• How can I tell who the Spam is from?

• How do “spammers” get my address?

• If I “unsubscribe” won’t the Spam stop?

Links

What are DNS blacklists?
DNS blacklists are lists of domains that are known to originate Spam. Many anti-spam software programs use these lists to control Spam by refusing any email that originates from one of these domains. DNS blacklists are usually maintained by anti-spam organizations or by individuals with an intense dislike for Spam. The difficulty with DNS blacklists is the need for objectivity in deciding when to blacklist a domain.

In order to know that a domain is producing Spam, the offence must be reported. Reporting Spam without any anti-abuse mechanism in place, however, leaves nothing to stop people from getting servers added to a DNS blacklist out of malice. The obvious solution would be to require a minimum number of reported incidents before blacklisting a server. This proves equally unsatisfactory however as a measure to stop Spam mail. Anyone who manages large mailing lists knows that a small percentage of people who subscribe subsequently accuse the sender of spamming them when they receive their email. Naturally, a company that sends out millions of legitimate commercial emails will receive more accusations of Spam than one that sends out a smaller amount of spam free bulk email.

• How big of a problem is Spam?

• What are DNS blacklists?

• What is an open relay?

• How can I prevent Spam?

• How does an email Spam filter work?

• I want to send spam free bulk email. How can I be sure my recipients don’t think I’m sending Spam?

What is an open relay?
Anyone who has travelled a lot has experienced the following: You check into your hotel. You connect to the Internet using the Ethernet socket in your hotel room. You try to send an email to the office, and your email client refuses saying “relaying denied”. What happened? Suppose your email address is you@foo.bar. Your regular email server, which may be named mail.foo.bar, knows all of the IP addresses of all of the machines connected to the Internet via the foo.bar domain. Should the mail.foo.bar forward email coming from another domain than foo.bar, this is referred to as “relaying”. Most ISPs do not allow relaying of email from untrusted domains, indeed from any domains but their own.

Your laptop computer was using an IP address allocated by your hotel’s DHCP server. Mail.foo.bar did not recognize this IP address, and refused to relay. There are a lot of poorly configured email servers however, that will let anyone use them to send email. An open mail relay becomes a channel for Spam, virtually “hijacked” by unscrupulous spammers who send large numbers of emails through them until they are discovered and banned, and move on to another open relay. Early versions of certain email servers did not stop spam email , but defaulted to open relaying when set up, so that there are many open relays available to spammers today. Recent versions of most email server products default to denying relaying in order to block junk email.

Other sites of interest