🚫 Blacklist / RBL Checker

An email blacklist (or RBL — Realtime Blackhole List) is a database of IP addresses or domain names that have been reported for sending spam or other malicious email. When a receiving mail server processes an incoming email, it queries these lists to decide whether to accept, reject, or flag the message. Being listed on a major blacklist like Spamhaus or Barracuda can cause your emails to bounce or land in spam folders across thousands of mail systems simultaneously.

Common reasons for blacklisting include: your mail server was compromised and used to send spam, high spam complaint rates from your email campaigns, sending to spam trap addresses (old/inactive email addresses maintained by blacklist operators), a previous owner of your IP having a poor reputation, or a misconfigured mail server. Even a correctly configured server can get listed if it shares an IP block with bad actors on a shared hosting or cloud platform.

First, fix the root cause — if your server sent spam, secure it and stop the source. Then submit a delisting request through the blacklist's official process. Most blacklists provide a delisting link in the check results. Review times vary: some are near-instant, others take 24–48 hours. Spamhaus requires the underlying issue to be resolved first. After delisting, monitor regularly to ensure you stay clean — recurring listings are harder to remove. OSH.co.za can assist with blacklist remediation.

IP blacklisting targets the sending server's IP address — the machine that actually delivered the email. Domain blacklisting targets the domain name in the email's envelope (return-path) or From header. Some blacklists use both. IP blacklisting is more common and directly affects deliverability. Domain blacklisting is used by URL-based filters (URIBL, SURBL) that scan links inside email bodies. You can check both by entering either an IP address or a domain name in the checker above.

For active email senders, weekly checks are recommended. If you send high volumes of email daily, consider daily monitoring or use an automated monitoring service. A new blacklist listing can appear at any time — catching it early prevents significant damage to your email reputation. Many DMARC reporting services also include blacklist monitoring as part of their dashboard. If you notice a sudden drop in deliverability or bounce rate increase, an immediate blacklist check is the first diagnostic step.