This guide presents the operation of RBLs, the questionable policy of some of them and the means to resolve a possible email block.

Preamble

• RBLs (Realtime Blackhole Lists) or DNSBLs (DNS Black Lists) are lists containing addresses / IPs / provider names / servers, known as major spammers.
• These are often large, generalized blacklists that help identify unwanted messages and their senders, 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 mail. 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 RBL, this means that Infomaniak's security system has detected suspicious or unwanted activities associated with this email address. This can include mass sending of unsolicited mail, participation in phishing campaigns or other malicious behaviors.

Resolving an email block (RBL)...

… if the error mentions your address and RBL

If you encounter errors of the type

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

when sending an email and you think it's a false positive, contact Infomaniak support.

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

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

… if the error mentions an organization like Sorbs or Barracuda

If you encounter errors of this type

554 5.7.1 Client host blocked using sorbs

or similar:

1. Follow the procedure of the mentioned organization (e.g. http://www.barracudacentral.org) to get your address removed from the list.
2. Temporarily switch your Internet service provider or connection method - WIFI vs 4G/5G - to send your messages.
3. Inform your contact and their email provider to take the necessary steps and/or to stop using an unreliable RBL.
4. Wait a few hours and try again.

Fewer and fewer professionals (ISP, hosts, etc.) use providers like Backscatterer / UCEPROTECT which are primarily profit-driven. There are many other highly effective lists, such as ABUSIX or SPAMCOP, which are well-maintained and genuinely aimed at fighting spam, one of the priorities of Infomaniak.