IP Address Blacklisting[/caption]
IPv4 address blacklisting is done to control spam and prevent malicious activities. Every blacklist has its own set of criteria for blacklisting IP addresses of email spammers, which could be based on technical factors, ISP policy, and evidence-based.
Technical blacklisting usually happens due to mail servers configuration issues, such as improper reverse DNS records and banner greetings, and mail servers operating within a range of suspicious IPv4 address blocks. ISP policy-based blacklisting is done when the receiving server decides not to accept emails from specific countries or ISPs, which are known for not following unsubscribe requests properly. Evidence-based blacklisting refers to those cases wherein the server has reliable proof to block an IPv4 address block because it has been involved in sending spam emails.
Most mailboxes identify blacklisted IPv4 address automatically and filter the email messages as spam, bounce the email, or drop it altogether. There are many tools available as well, that can help you to check your sender’s IPv4 address against renowned blacklists. This way, you can find out where your IP is listed; the blacklist website will have the information regarding why your IPv4 address is blacklisted and how you can de-list it.
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DNS-Based Blacklist[/caption]
Some local blacklists may not have an effect on your deliverability, but they may still affect your credibility. There are real-time blacklists as well, which means that your IPv4 address can be listed and de-listed of the blacklist anytime and will not necessarily stay on the list for a long time. However, there are some major blacklists, which block your emails and make it very difficult to get your IP address de-listed.
Spamhaus, for instance, is an international organization that tracks email spammers and spam-related activities and blocks the IPv4 addresses and domains as it deems necessary. Many large mailbox providers use Spamhaus to filter spam emails. You can find the option to check if your IPv4 address or domain is blacklisted on the Spamhaus site. They also provide information on what to do if your IP address or domain is listed on their database.
You can also check the DNS-based blacklist information on the DNSBL site to see whether your deliverability problems are due to IP blacklisting. However, note that being listed with a DNSBL service does not necessarily mean that your IPv4 address is a source of spam. Some mail servers do not accept email from IP addresses based on the country or connection type. You can also ask the DNSBL service that has blocked your IP address to remove the entry. Some blacklists may even remove your IPv4 address from their list automatically after their spam campaigns end.