Transactional Email Providers Compared: Costs and Pitfalls from Zero to 100K Emails

Choosing a transactional email provider becomes a major decision at scale, as pricing structures and hidden costs can force costly migrations. A detailed cost comparison across Resend, Postmark, SendGrid, Amazon SES, and Mailgun reveals significant differences in free tiers, overage rates, and add-on fees. Amazon SES underwent a major pricing overhaul on July 21, 2026, replacing its flat-rate model with three tiered plans and discontinuing free-tier access for new signups, making much existing advice outdated. At 100,000 emails per month, costs range from around $16 with SES Essentials to over $126 with Postmark, depending on plan and usage patterns. Each provider carries a specific gotcha — such as Postmark's zero-overage free tier, SendGrid's Pro-only dedicated IPs, and Resend becoming the priciest option at high volumes — making early provider selection a strategically important choice.