This guide explains how RBLs work, the questionable policies of some of them, and how to resolve any potential email blocking issues.

Introduction

• RBLs (Realtime Blackhole List) or DNSBL (Black List DNS) are lists containing addresses/IP addresses/provider names/servers that are known to be major sources of spam.
• These are often large, general blacklists used to identify messages considered undesirable and the senders of those messages, and are maintained by certain providers (smtpcheck, uceprotect: non-exhaustive list)…

Adding the email address to the RBL

When an email address is identified as belonging to an unwanted sender, it is blocked to prevent the receipt of unsolicited messages. A block in the RBL does not expire. Addresses will be listed indefinitely.

If you receive a message indicating that your email address is blocked by an RBL, it means that Infomaniak's security system has detected suspicious or undesirable activity associated with that email address. This may include sending large numbers of unsolicited messages, participating in phishing campaigns, or other malicious behavior.

Resolving an email block (RBL)…

… if the error message mentions your address and RBL

If you receive error messages like the following:

anna.a@domain.xyz is RBL blacklisted - http://chk.me/rbl

If you encounter this issue when sending an email and believe it is a false positive, contact Infomaniak support.

To prevent your email address from being blocked by the RBL blocking system in the future, follow these best practices for email usage:

1. Do not send unsolicited messages or mass messages to unknown recipients.
2. Regularly sort the list of recipients used.
3. Do not participate in phishing or cybercrime activities.
4. Ensure the highest level of security where your emails are used:
   1. strong password
   2. up-to-date software
   3. up-to-date operating system (iOS, Android, Windows, macOS, etc.)
   4. up-to-date configuration of the associated domain

… if the error mentions an organization such as Sorbs or Barracuda

If you receive errors such as

554 5.7.1 Client host blocked using sorbs

or similar:

1. Follow the procedure outlined by the organization in question (for example, http://www.barracudacentral.org) to have your address removed from the list.
2. Temporarily change your internet service provider or connection method – Wi-Fi vs. 4G/5G – to send your messages.
3. Inform your recipient and their email provider to take the necessary steps and/or stop using an unreliable RBL.
4. Please wait a few hours and try again.

Fewer and fewer professionals (ISPs, hosting providers, etc.) are using service providers such as Backscatterer / UCEPROTECT, whose primary purpose is financial gain. There are many other very effective lists, such as ABUSIX or SPAMCOP, which are well-maintained and whose real goal is to fight spam, one of Infomaniak's priorities.