The Backscatterer blacklist: the easy way out

Have you blacklisted your IP address and found it listed on the Backscatterer list? Don’t panic, we’ll explain everything.

The RBL Backscatterer (RBL for Realtime Blackhole List) penalizes domain names associated with mail servers that send error messages to external addresses without checking that the error corresponds to mail actually sent from these addresses.

Here’s a concrete example: a spammer sends an e-mail to the address fausseadresse@societeA.com, using as the sender address an address that does not belong to him: expediteur@societeB.com. The mail server of the societeA.com domain doesn’t check that the e-mail sent is legitimate and has really been sent from the mail server of the societeB.com domain. It sends an error message with a copy of the original e-mail to expediteur@societeB.com. The person behind the expediteur@societeB.com mail therefore receives an error message even though he never sent anything. The IP of the mail server for the societe1.com domain is then eligible to be added to the Backscatterer blacklist.

Delisting the RBL Backscatterer

You can’t delist yourself. There is no delisting procedure. The only solution is to adjust your mail server. The IP is then removed as soon as this type of spam is not detected. You can test your IP address by following this link: http: //www.backscatterer.org/index.php?target=test

How to avoid the RBL Backscatterer?

You should avoid sending an error e-mail when an e-mail is received at a non-existent address. The best thing to do is to refuse the e-mail immediately during the SMTP transaction.

Under Postfix, in the main.cf file change: smtpd_error_sleep_time = 0

Deliverability glossary

Blacklist: this is an online database of IP addresses and domain names that have been reported as transmitting spam or phishing. These blacklists can be used by mail servers for anti-spam processing.

IP address: in Internet Protocol, an IP is a unique address that designates a server on the Internet or a local network. To find out more about IP addresses: https: //fr.wikipedia.org/wiki/Adresse_IP