The SaaS Podcast, Episode 456

Mailtrap: From 20,000 Email Disaster to 7-Figure SaaS – with Sergiy Korolov
Host: Omer Khan | Guest: Sergiy Korolov (Co-CEO of Railsware and Co-founder of Mailtrap)
Date: October 9, 2025

Overview

In this episode, Omer Khan sits down with Sergiy Korolov to discuss the remarkable journey of Mailtrap—how an accidental email disaster led to building a 7-figure SaaS used by over 100,000 active users each month. The conversation covers the evolution from a free internal tool to a full-featured email platform, the lessons (and mistakes) in finding product-market fit and pricing, and how deep community trust and deliberate growth outpaced competitors. Sergiy shares insights on user research, bold product decisions like mandatory surveys, and how “fake features” validated demand. The discussion is hands-on, honest, and packed with practical takeaways for SaaS founders.

Key Discussion Points & Insights

1. The Accidental Origins of Mailtrap

• Genesis: Mailtrap was born after Sergiy’s team accidentally sent 20,000 test billing emails to real customers, creating confusion and anger ([00:09]–[06:27]).
  • Sergiy: "It was the huge fuck up... customers were angry and they didn’t understand what happened." ([06:27])
• Solution: Built an internal tool to block outgoing emails from staging environments—soon made public and widely adopted in the Ruby on Rails community.
• Organic Growth: Entirely word of mouth; no marketing for five years; over 200k users before monetization.

2. Transitioning from Tool to Product & a Business

• Longtime Free Tool: For five years, Mailtrap stayed a side project, supported by a skeleton team ([12:38]–[14:21]).
• Trigger for Monetization: Rising requests for features and infrastructure costs led to introducing paid plans.
  • Initial monetization was basic, limiting emails/features for free users.
• User Numbers at Monetization: ~200,000 signups, 20-25k active users at the time ([14:25]).

3. Data-Driven Decision Making: Pricing & Product

• Emphasis on Research: Instead of guessing pricing, Sergiy’s team ran over 100 customer interviews, dissected usage data, and conducted segmented surveys ([15:07]–[17:24]).
  • Sergiy: “We have a lot of assumptions...but then you need to measure the results.” ([15:57])
• Finding: Features/development efforts owners assume are valuable may not drive purchases; data is critical for prioritization.
• Surprising Insight: Smoother, lower-click onboarding did not substantially impact conversions—the core value mattered more ([17:37]):
  • Sergiy: “If there is a core value… even if you have 20 more clicks, users tend to make those clicks.”

4. Growth Tactics: Organic, Community, and Then Content

• Early Growth: Purely community-driven, word of mouth; active involvement in developer communities ([18:54]).
• Hitting a Plateau: Eventually, organic growth slowed; Mailtrap hired marketers, started a blog, and ramped up educational content—leading to renewed exponential growth ([19:38]):
  • *"We had no blog, no social media...focus on content had a very positive influence.”

5. Mandatory Signup Surveys: Counterintuitive Results

• Required Signup Survey: Made survey completion mandatory during signup to better segment users and gather actionable data ([21:43]–[21:43]).

  • Survey included: User intent (business, pet project, education), role, and marketing channel.

• Main Finding: Conversions were unaffected—deep insight gained without user drop-off ([26:51]):

  • Sergiy: “Nothing has changed…But we had a lot of benefits after that.”

• Benefits: Ability to filter user cohorts, improve product/marketing decisions, see where marketing traffic is being wasted ([28:58]):

  • *"You bring a lot of traffic, but you bring a lot of folks who are doing pet projects and they do not convert..."

6. Validating New Features with “Fake” Product Elements

• Testing Demand Smartly: Instead of building first, Mailtrap added a non-functional "Email Campaigns" button that linked to a Typeform ([29:21]).
  • Received 300+ replies in weeks—clear, valuable signal to prioritize feature development ([31:17]):
  • Sergiy: “No Amazon codes, no rewards...just put the survey and again a lot of insights, prioritization from the feature perspective...”

7. The Shift to Sending Emails: A Brand and Technical Challenge

• Pivot to Sending: User demand drove Mailtrap to go beyond sandbox/testing and offer full email delivery—making them compete with SendGrid, Mailgun, etc. ([32:04]).
• Difficulties:
  • Brand Perception: Trust built on “not sending” emails now had to persuade users they could deliver reliably ([32:47]).
    • *"Before Mailtrap was about not sending email to the inbox… now we guarantee you will send..."
  • Technical: Fighting spam, scams, security threats—“the whole Internet wants to hack you.” Major investment in infrastructure and anti-spam ([32:47]).
• Market Logic: Sending is a much bigger (and less replaceable) market than testing ([35:44]).
• User Feedback: Many customers were dissatisfied with competitors’ lack of transparency and support ([37:22]):
  • Inspired Mailtrap to build better analytics, deliverability tools, and actionable feedback for users ([40:54]).

8. Insights on AI, Low-Code, and Developer Productivity

• View on AI/Vibe Coding: Useful for prototyping, code scaffolding, but not for scaling to complex products ([41:07]–[48:54]).
  • Sergiy: “AI is just a tool that helps good engineers to be productive… it’s not a replacement...just a 20-50% boost.” ([49:43])
• Pattern Recognition: Each tech leap (from assembler to frameworks to AI) brings incremental, not revolutionary, productivity ([49:43]).

Notable Quotes & Memorable Moments

• On the accidental 20,000-email send:

  • “It was the huge fuck up...customers were angry and they didn’t understand what happened.” (Sergiy, [06:27])

• On product-market fit and community:

  • “Zero marketing. You find your market fit… it’s a combination of the concept ‘eat your own dog food.’” (Sergiy, [08:12])

• On the effectiveness of required signup surveys:

  • “Nothing has changed… But we had a lot of benefits after that.” (Sergiy, [26:51])

• On necessary, but sometimes counterintuitive, design decisions:

  • “If there is a value…even if you have 2 more clicks or 20 more clicks… users tend to make those clicks.” (Sergiy, [17:37])

• On fake product features for validation:

  • “We just put the email campaign menu item...when you click it was just a Typeform… In a few weeks got 300 replies.” (Sergiy, [31:17])

• On AI and developer productivity:

  • “AI is just a tool…good for documentation, analyzing code… not a replacement for engineers.” (Sergiy, [49:43])

• Sergiy’s Favorite Quote:

  • “Master your craft every day.” ([03:54])

Timestamps for Key Segments

• [00:09–06:27] — Origins: The 20k email disaster and creation of Mailtrap
• [12:38–15:07] — Deciding to monetize, first pricing attempts
• [15:07–17:37] — Deep user research, learning from analytics
• [17:37–18:54] — Surprises: Onboarding simplification’s little impact
• [19:38–21:06] — Breaking the growth plateau with content marketing
• [21:43–26:51] — Implementing required signup surveys, results
• [29:21–32:04] — Validating demand via “fake” feature, using surveys as product research
• [32:47–36:59] — Brand and technical challenges in moving from email testing to sending
• [37:22–40:54] — User feedback informing product development, competitor pain points
• [41:07–49:43] — Discussion on AI, low-code tools, developer productivity

Lightning Round Highlights ([52:10–55:47])

• Best business advice: “Go with the flow.” (Sergiy, [52:15])
• Book recommendation: The Power of Now by Eckhart Tolle ([52:20])
• Key founder attribute: “You never stop.” ([53:32])
• Favorite productivity tool: Spotlight search/command line interfaces ([53:38])
• Fun fact: Sergiy was once a professional swimmer, part of his country’s Olympic reserve ([54:52])
• Passion outside work: Sports, especially snowboarding, biking, and time with family ([55:15])

Conclusion

This episode is a masterclass in humility, validation, and thoughtful SaaS growth. Sergiy and team demonstrate how understanding your users—deeply—at every stage multiplies your product's value. The counterintuitive takeaways (mandatory surveys don't crush conversions, more clicks sometimes don’t matter, “fake” product buttons are a viable research tool) provide pragmatic lessons, and the story of evolving Mailtrap’s brand and product is both cautionary and inspiring. The episode is a must-listen for founders seeking sustainable SaaS success.