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.

In the global landscape, North American inbox placement rates (IPR) experienced significant declines with an 8% drop, bringing in inbox placement rates closer to 79%.  

The Asia-Pacific region’s deliverability rates declined by 14% in the second half of 2011 with only 67% of all mail reaching its intended inbox destination, while in Central and Latin America only 72% of emails made it to the inbox.  

Return Path client services director for Northern Europe Richard Gibson said the key to improving deliverability rates was to manage reputational factors.

Marketers need to own the factors that impact on their reputation, such as complaint rates, and work out why their emails aren’t making it through to the inbox.”

To improve performance, marketers first need to look at their deliverability rates, then modify factors such as email frequency and management of old subscribers to improve their reputation with ISPs.

He said 100% IPR was achievable, but brands need to be aware that ISPs are raising the bar on reputation metrics – making it harder to get into the inbox.  

According to the majority (53%) of companies that took part in the Econsultancy / Adestra Email Marketing Census 2012, having a clean, up-to-date email list has the biggest impact on improving IPR.

The next most cited factors are focus on relevance of email to recipients (50%) and reputation of sender (38%).

In a separate study, Return Path analysed a sample of 40,000 Gmail mailboxes, and over 110m messages from July 1 2011 to December 31, 2011.

It found that 93% of all Gmail subscribers now have priority inbox enabled, up 15% from Return Path’s previous study. But Gmail inbox placement rates declined to 79% with 21% of mail being delivered to the spam folder.

Out of the 79% of mail delivered to the inbox, only 8% were marked priority, a 54% decline compared to Return Path’s previous study.