Nearly 18% of marketing emails miss inboxes, study finds

Sinch Mailgun has published research showing that nearly 18% of marketing emails fail to reach inboxes.

The findings are based on analysis of more than 400 billion emails sent in 2025 and a survey of more than 1,200 email senders worldwide.

The report suggests email remains a core sales and customer retention tool for many businesses, despite persistent problems with delivery and measurement. It found that 78% of respondents view email as critical to business success, while fewer than half can confidently measure its return on investment.

That gap between email's perceived value and its execution sits at the centre of the study. Weak deliverability practices, limited performance measurement and uneven use of artificial intelligence are reducing returns for organisations that continue to invest heavily in email.

According to the report's estimates, nearly a fifth of potential return on investment is at risk when messages do not land in inboxes. Even so, 79% of respondents said they plan to maintain or increase spending on email.

Return gap

The data points to strong returns for companies that do track results. Sixty per cent of companies measuring email ROI reported returns of more than $10 for every $1 spent, and more than one in 10 said returns reached 40:1.

Yet the survey also found that many teams still lack the systems or confidence to measure those returns properly. That makes it harder for marketing departments to determine whether poor results stem from message content, audience targeting, sending frequency or basic deliverability issues.

The study also showed year-on-year improvement for some organisations. Nearly half of respondents, or 49%, said email performance had improved compared with the previous year.

Sinch Mailgun presented the findings as evidence that email remains one of the more resilient digital marketing channels, but one in which operational weaknesses can directly affect revenue. Messages that fail to arrive cannot generate opens, clicks or sales, and the report argues this is a basic but often overlooked issue.

AI use

Artificial intelligence featured prominently in the research, though the findings suggest adoption has so far centred on simpler tasks. Forty-six per cent of respondents said AI improves speed and efficiency, while 41% said their teams use it to generate email content.

Higher-value uses appear less common. Optimisation, segmentation and deliverability remain underused, even though organisations applying AI more effectively are significantly more likely to report stronger email performance.

That pattern suggests many marketing teams are still using AI as a production tool rather than a decision-making tool. In practice, that means help with drafting subject lines or body copy is more common than using machine learning to decide who should receive a message, when it should be sent or how likely it is to damage sender reputation.

For businesses sending email at scale, those decisions can determine whether campaigns reach active customers or are filtered out before they are seen. The report's benchmarks cover 10 high-volume industries, though Sinch Mailgun did not identify those sectors in the material released.

Ginger Kidd, Vice President Marketing & Communications APAC at Sinch, said the findings reflect pressures facing marketers in the region.

"APAC businesses rely heavily on email to drive sales, loyalty and customer experience, but many are not set up to capture its full value," Kidd said. "What we see in this data reflects what's happening locally: brands are investing in email and seeing strong returns, yet many messages still never reach inboxes. In a market as competitive and cost-conscious as Australia, marketers simply can't afford for emails to get lost. When budgets are under pressure, fixing deliverability is one of the fastest ways to unlock more value from existing spend."

Regional focus

Kidd said the research also shows a common pattern across APAC markets in how marketers are adopting AI.

"Across the diverse markets of APAC, we're seeing a common theme: marketers are enthusiastically adopting AI, but the initial focus has primarily been on content creation. The true opportunity now lies in using AI for smarter decision-making - for instance, who to send to, how often and with what level of risk. This strategic shift is key to ensuring every campaign improves performance, not just adds volume.

"The most sophisticated teams are already using AI to predict which subscribers are at risk of disengaging, to fine-tune send times and to protect sender reputation. That's where we're seeing a real uplift in performance, not just faster content production."

Sinch said it handled more than 900 billion customer interactions annually across messaging, email and voice in 2025, and reported net sales of USD $3 billion. It said the Mailgun report draws on one of the larger datasets available on email sending patterns and marketer sentiment.

The findings suggest that for many organisations, the question is no longer whether email works, but whether they can manage the basics well enough to secure the returns they expect.