More stringent ISP filtering and deteriorating sender reputations mean that global email deliverability declined by 6% to 76.5% in the second half of 2011.
Email certification company Return Path announced the findings in its Global Email Deliverability Benchmark report, which monitored data from 1.1m campaigns.
These covered 142 ISPS in North America, Central and Latin America, Europe, Asia and the Pacific territories from July through December of 2011.
In the UK, 83% of marketing emails reached the inbox, with 7% being delivered to the spam folder and 10% registered as missing or blocked.
The study suggests that an increased volume of emails also contributed to the fall in delivery rates, as overwhelmed consumers are more likely to mark emails as spam rather than unsubscribing.