Some 21% of permission emails from legitimate senders around the world failed to reach the inbox during the year-long period from May 2014 to April 2015.
Email marketing decision-makers from the US, Germany and France believe that an average of 60% of their emails are delivered to the correct inboxes.
List growth was the most common hurdle, cited by the majority of respondents.
Email overload has a negative effect on consumers, cited as their top reason for unsubscribing from a list.
Other tactics marketers expected to use to boost email relevancy included centralizing email, mobile and social subscriber data.
What marketing professionals had to say about the email-related services their teams are using to overcome limitations in expertise and time in 2011.