Which Blacklists Does Gmail Use? New Infographic and Webinar.

Return Path proudly holds the Return Path certified whitelist in the arsenal of tools we can provide clients. With such a whitelist, it’s easy to feel like the “white hat” of email marketing. Despite a world of spam and poor marketing practices, Return Path champions the good senders. You can almost imagine Return Path as The Lone Ranger defending the Old West. Well, almost.

But with every “white hat,” there is always a “black hat”—in our case, the appropriately named blacklist. A blacklist is a list of IP addresses and domains that have been reported as “known” sources of spam. In essence, blacklists promote a safe, spam-free email environment, but to email marketers, they can feel like the kiss of death. We all know that blacklists can negatively impact inbox placement rates, but by how much? What blacklists are used by Mailbox Providers? If you are dealing with blacklisting problems, never fear. We looked at blacklisting trends for permission-based marketers for all of 2013, and compiled an ultimate guide to blacklists.

While there are hundreds of well-known public blacklists, we have identified the thirteen most prominent ones in the infographic. Return Path Reputation Network Blacklist, SpamCop, psbl.surriel.com, cbl.abuseat.org, pbl.spamhaus.org, sbl.spamhaus.org, xbl.spamhaus.org and ubl.unsubscore.com are the most common IP-based blacklists. Dbl.spamhaus.org, URIBL and SURBL are the most common domain-based blacklists, and dnsbl.ahbl.org and invaluement.com are popular blacklists that consider both domain and IP reputation.

Although Gmail does not publicly disclose which blacklists they use, our data shows correlations between Gmail and the following blacklists:

  • pbl.spamhaus.org - Pbl.spamhaus.org is Spamhaus’ Policy Block List (PBL), which helps networks enforce their Acceptable Use Policy for dynamic and non-MTA customer IP ranges. Spamhaus indicates on their website that the PBL is not a blacklist, and that it is perfectly normal for dynamic IP addresses to be listed on the PBL. Spamhaus insists that PBL listings do not prevent email sending unless your email program is not authenticating properly when it connects to the Mailbox Provider or your company’s mail server, which can occur if you have not turned on SMTP Authentication. Gmail seems to utilize the PBL, and placement on the PBL led to a 58% average decline in Gmail Inbox Placement Rate.  
  • sbl.spamhaus.org - The Spamhaus Block List (SBL) is a database of email addresses which Spamhaus identifies as associated with spam. Gmail seems to utilize this list, and blacklisting on the SBL led to a 21% average decline in Gmail Inbox Placement Rate. According to our research, the SBL blacklisted most IPs for either 1 – 3 or 6 days.
  • Composite Blocking List (cbl.abuseat.org) - The Composite Blocking List (CBL) is an IP-based blacklist that appears to be utilized by Gmail. Blacklisting on the CBL led to a 4% average decline in Inbox Placement Rate. According to our research, 70% of the blacklisted IPs remained on the CBL for 1 – 2 days, 24% were on it for 7 – 8 days and 5% remained for 14 days.
  • xbl.spamhaus.org - Xbl.spamhaus.org is Spamhaus’ exploit and botnet filter, which lists IP addresses coming from computers hijacked with illegal third party exploits, including open proxies, worms and viruses. Blacklisting on the XBL generated a 3% average decline in Gmail Inbox Placement Rate, and most IPs placed on the XBL remained for 1-2 days or 7-8 days. With the shutdown of NJABL in 2013, the only data source the XBL currently uses is the CBL, so any declines in inbox placement as of this writing will be the same.

According to our research, Gmail does not appear to use the following blacklists:

If you would like to learn more about how blacklists affect your email program, check out The Ultimate Guide to Blacklists webinar. Equipped with the tools you need to understand blacklists, you can eliminate them as a foe and increase inbox placement at Mailbox Providers like Gmail.