Landing on an email blacklist—a collection of IP addresses and domains flagged as "known" sources of spam—can greatly affect a brand's ability to reach consumers, according to a recent report from Return Path.

For example, provider Spamhaus's blacklists significantly influence inbox placement decisions at Gmail, sometimes preventing more than half of a blacklisted brands' Gmail subscribers from receiving their messages, the study found.

Below, additional key findings from the report, which was based on an analysis of 20,000 blacklisting events affecting large email senders.

Causes and Timing 

• Blacklisting events are often associated with the introduction of new email lists from third-party sources, as well as with campaigns sent to long-inactive subscribers.
• The holidays are the most common time to land on a blacklist, with 49% of blacklistings occurring November to December, likely because holiday shopping is such an important revenue opportunity for many brands that marketers are more inclined to adopt aggressive tactics to maximize their reach.
• The length of time that a brand remains blacklisted depends in large part on the list provider. For example, 86% of blacklisting at SpamCop lasts a day or less, whereas 25% of blacklisting at Spamhaus lasts 7-8 days.