Take a SaaS company sending 200,000 transactional emails a month: if inbox placement drops from 95 percent to 85 percent, that is 20,000 messages that quietly vanish, routed to spam or swallowed by filters before anyone notices. Password resets, onboarding sequences, billing alerts, all technically “sent” but never actually seen.
At that volume, even a conservative estimate of the revenue tied to each email puts the annual loss well into six figures. Most product teams have no idea it is happening.
The failures nobody reports to leadership
A user writes in saying they never received an invoice, and the support team logs it as a billing issue. A trial user signs up and never comes back, so it shows up as an activation failure. A paying customer gets locked out because a password reset did not arrive, and someone in engineering resends it manually before moving on.
These problems get scattered across departments, each one small enough to dismiss on its own, and none of them get categorized as email infrastructure failures. But taken together they form a pattern that is surprisingly common. A 2025 Mailgun survey found that 48 percent of email senders say their biggest challenge is simply keeping messages out of the spam folder. One case study published by IBM Think profiled a company that watched its open rates collapse from 80 percent to 10 percent, and nobody on the team could explain why.
The direct revenue hit
Most of what makes a SaaS product feel reliable happens through transactional email: welcome messages, verification codes, payment receipts, trial expiration reminders. This is not marketing. It is product functionality delivered through the inbox, and research consistently shows these messages generate roughly eight times the engagement of a promotional campaign. So when they fail, the damage is outsized.
The onboarding window is a good example. Studies on SaaS trial conversion have repeatedly found that if a new user does not reach an activation moment within the first 72 hours, the probability of conversion drops below five percent. A welcome email that lands in spam does not just delay that moment. For the share of signups who will never think to check their junk folder, it eliminates it entirely.
There is also the problem of involuntary churn, which is one of the more expensive failures that nobody talks about. When billing notifications land in spam, customers miss renewal alerts and failed charge warnings. Finance sees the churn and blames the payment processor. Product sees a retention dip and blames feature engagement. Meanwhile, the actual cause sits in the email layer, unmonitored and undiagnosed. Industry researchers estimate that undelivered emails cost US businesses roughly $60 billion a year in lost potential revenue.
The compounding costs nobody calculates
What makes deliverability failures especially damaging is how they feed on themselves. A drop in inbox placement leads to lower engagement, which signals to mailbox providers that recipients do not value the messages, which triggers even more aggressive filtering. Reputation scores decline, open rates fall further, and fewer emails get through. The whole thing accelerates.
Meanwhile, engineers spend hours chasing symptoms without the right observability tools, support agents handle the same “I never got my email” tickets on repeat, and product managers launch feature experiments to fix what is actually an infrastructure problem. All of that pulls attention away from the roadmap.
Why product teams specifically bear the burden
Onboarding, activation, password resets, billing alerts: product teams own all of these. What they rarely own is the email infrastructure those flows depend on. That usually lives somewhere between engineering and DevOps, if it has a clear owner at all.
Most SaaS organizations have zero dedicated deliverability monitoring. Problems surface through user complaints and mysterious drops in conversion funnels, not through dashboards. The 2025 Validity benchmark reports that the software sector has some of the lowest email deliverability of any industry, hovering around 81 percent. That means roughly one in five legitimate emails from software companies never reaches the intended recipient.
Where the industry is heading
The tightening of sender requirements by Google, Yahoo, and Microsoft through 2024 and 2025 forced a reckoning. Authentication protocols that were once considered best practices became mandatory, and the providers serving this market have responded by carving out increasingly distinct positions.
Twilio SendGrid remains the largest player in enterprise email, while Amazon SES appeals to teams already deep in the AWS ecosystem who want raw throughput at the lowest possible cost. Postmark, acquired by ActiveCampaign in 2022, has built a loyal following among developers who prioritize delivery speed over marketing features. Mailgun continues to serve a broad audience, though its acquisition by Sinch and recent pricing changes have pushed some users to explore alternatives.
Mailtrap has taken a different route. The company started in 2011 as an internal tool at Railsware, a Ukrainian product studio whose early clients included Calendly, but today it operates as an email delivery platform for high-volume SaaS senders.
The company claims over two million signups and 150,000 active customers, according to figures cited in a 2025 SaaS Club podcast interview with co-CEO Sergiy Korolov. Railsware, which has never taken outside funding, reached $17 million in revenue in 2024 and appeared on the Inc. 5000 list of fastest-growing private companies.
The broader market remains fragmented. No single provider dominates across every use case, and the gap between what large platforms offer at scale and what growing SaaS companies actually need has created room for more focused solutions.
What this actually means for product teams
Nobody gets promoted for improving inbox placement rates. But the companies that treat email delivery as a product reliability problem, something on par with uptime or latency, tend to be the ones that scale without the mysterious activation dips and unexplained churn that plague their competitors.
At scale, those failures compound into real revenue loss, the kind that shows up in your metrics long before anyone traces it back to the inbox.
For more helpful tips, check out the rest of our site and learn more.
