As an indie SaaS founder, sending hundreds of emails a day can be both an exciting milestone and a serious technical challenge. Email deliverability—the science and art of landing in the inbox and not the spam folder—is critical when you depend on personalized email outreach to drive user signups, provide onboarding support, or manage transactional communications. With Gmail, Outlook, and other providers tightening spam filters, using a robust and reputable email gateway or relay service can mean the difference between a thriving product and a struggling one.
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TL;DR
If you’re an indie SaaS founder sending high volumes of email, reliable email gateways and relays are essential for keeping your messages out of spam folders. Services like Postmark, Mailgun, and Amazon SES are trusted for deliverability, scalability, and integration features. Some platforms are better at transactional email, others at marketing, and some excel in both. This article breaks down the top 5 email relays used by indie SaaS builders to maintain high inbox placement when sending hundreds of emails per day.
1. Postmark: Precision Focus on Transactional Emails
Postmark is widely praised in the indie SaaS community for one reason: speed and deliverability of transactional emails. From password resets to confirmation messages, Postmark’s infrastructure is built for timely and reliable message delivery.
- Deliverability: Postmark is laser-focused on transactional emails and maintains one of the best reputations among receiving servers.
- Speed: In many cases, emails are delivered within seconds due to low latency servers worldwide.
- Authentication: Supports SPF, DKIM, and DMARC to maintain a solid sending reputation.
- Segregated IP pools: Marketing and transactional emails don’t share the same infrastructure, so transactional emails stay clean.
While it’s not the first choice for newsletters or broad marketing outreach, Postmark is ideal for founders who care deeply about the trustworthiness of core product emails.
2. Mailgun: A Flexible Developer-Friendly Giant
Mailgun has long been a staple among developers seeking programmatic access to email services. Its flexible API, powerful analytics, and strong feature set make it a compelling solution for most SaaS platforms.
- Flexibility: Built for developers, and supports RESTful APIs, SMTP, and custom webhooks.
- Deliverability Tools: Includes inbox placement predictions, spam filter testing, and deliverability consulting.
- Scalable: Hundreds to millions of emails per day, depending on your growth and plan level.
- IP Warmup: Helps you manage dedicated IPs and maintain reputation while ramping up email volume.
Its complexity might be overkill for smaller startups, but if you’re growing fast and need granular control—Mailgun fits the bill.
3. Amazon SES (Simple Email Service): Power and Economy Combined
For indie founders who are technically inclined and cost-conscious, Amazon SES offers unbeatable pricing paired with enterprise-grade performance. Backed by AWS infrastructure, SES is one of the most scalable email services available today.
- Affordability: Among the cheapest email relay services, costing fractions of a cent per message.
- Reliability: Huge sender reputation thanks to AWS infrastructure, but requires setup diligence.
- Custom Configuration: Allows custom domain authentication (SPF, DKIM), dedicated IPs, and analytics integration.
- API + SMTP: Works seamlessly whether integrated through SMTP or the AWS API gateway.
While SES is perhaps the most powerful on this list, it does demand careful configuration and maintenance. Many indie founders pair it with UI-centric tools like Sendy or Postal to improve usability.
4. SendGrid: Marketing-Friendly With Strong Infrastructure
SendGrid offers a middle ground between powerful infrastructure and user-friendly marketing features. Although originally known for transactional emails, it’s evolved into a full-service email delivery platform with a sleek dashboard and robust analytics capabilities.
- Reputation: Now owned by Twilio, SendGrid is a well-known name and holds a strong receiver-domain reputation.
- Versatile Use Cases: Suitable for both transactional and marketing emails.
- Email Builder: Drag-and-drop editor helps non-technical teams create HTML newsletters easily.
- Analytics and Testing: Includes A/B testing, engagement tracking, and deliverability stats.
SendGrid might not offer the ultra-focused transactional power of Postmark or the raw backend access of SES, but it’s a balance of power and approachability that works well for SaaS teams scaling between product and marketing functions.
5. Resend: A Newcomer Built for Developers
Resend is one of the newer players in the game, but its simplicity and developer-first approach have already captured the trust of many indie SaaS builders. It’s built to be intuitive and integrates natively with modern frameworks like Next.js.
- API Simplicity: Designed for developers; fewer configuration steps than Mailgun or SES.
- Ultra-Lightweight: No bulky marketing features. Just clean, effective transactional email delivery.
- Growing Community: Backed by a rapidly expanding developer ecosystem and strong documentation.
- Open Source Compatibility: Plays well with modern dev stacks and open standards.
If you’re an early-stage indie founder that needs reliable deliverability without climbing the complexity cliff of bigger providers, Resend is worth a strong look.
How Indie Founders Choose the Right Gateway
Most indie SaaS builders make their email relay choice based on three core factors:
- Deliverability: Does the service maximize inbox placement, even at scale?
- Integration: How easy is it to plug into your stack—be it Python, Node.js, or serverless frameworks?
- Features vs. Simplicity: Do you need dashboards and testing tools, or just reliable endpoints?
Pricing, customer support, analytics, and IP management also factor into long-term decisions. Many founders start with a service like Postmark or Resend for their simplicity, and either switch to Mailgun or SES as they scale, or integrate both based on email type.
Additional Tips for Avoiding Spam Filters
Choosing the right relay is just half the battle. Here are a few expert tips indie SaaS founders use to stay out of spam folders:
- Set up SPF, DKIM, and DMARC correctly from day one.
- Use a custom sending domain and avoid generic free domains like Gmail or Yahoo.
- Warm up your IP address before rapidly increasing volume.
- Keep your email copy clean—avoid spammy language and overuse of emojis or all-caps.
- Ask users to whitelist your sending domain during onboarding.
Conclusion
Deliverability is one of those backend challenges that can quietly tank your SaaS if not given proper attention. Each of the top 5 gateways mentioned—Postmark, Mailgun, Amazon SES, SendGrid, and Resend—brings its own strengths, depending on your goals, stack, and technical bandwidth.
Whatever you choose, the key is to monitor results regularly, maintain a clean sending reputation, and adapt quickly as you scale. In a world where one bad spam designation can lock down your customer pipeline, choosing a solid email delivery provider is a decision that deserves strategic importance.
