Inbox Issues: How Email Deliverability Problems Impact Revenue, Customer Retention, And More

For as much as marketers know the importance of email marketing, it’s still shocking to read stats like recent ones from Kickbox, which found that nearly two-thirds (64.8%) of businesses say deliverability issues have made an impact on either revenue or customer retention.

“Poor email deliverability — whether it’s getting blocked, bounced, or sent to spam instead of landing in the inbox — is often a reflection of a sender’s practices and reputation,” says the “Email Deliverability: The Cost of Missing the Inbox in 2025” report. “It doesn’t just impact open rates — it drains marketing budgets, cuts into revenue, and erodes customer trust.”

Spam filters were seen as the biggest challenge, far ahead of low engagement, email data-quality, high bounce rates, and poor sender reputation. Still, with many of those being “symptoms of deeper deliverability problems,” as Kickbox puts it, email list verification from services like Clean Your Lists take on vital importance. Particularly with, as one study estimated last year, the cost of undelivered email costing businesses more than $59 billion a year.

The Kickbox survey found that 40.2% only verify their lists monthly, which Kickbox says leads to “higher risks of challenges with poor inbox placement and lower engagement rates.”

(Source: Kickbox)

“Email deliverability issues can directly impact a business’s bottom line, affecting both revenue and customer retention,” the report says. “If a brand spends $10,000 per month on lead generation and 15% of those leads never receive an email, that’s $1,500 per month in wasted ad spend.”

For more information about how to improve your email deliverability, download A Beginner’s Guide to Email Marketing by Mirabel’s Marketing Manager: