How to Choose the Right ESP in 2025

Why Your ESP Choice Matters

Your email service provider is the backbone of your email program. It affects deliverability, developer productivity, cost efficiency, and ultimately the success of every email you send. Switching ESPs is costly and disruptive, so getting the choice right upfront saves significant pain later.

The ESP landscape in 2025 is more diverse than ever. Legacy platforms like Mailchimp and SendGrid compete with modern alternatives like Brew, Resend, and Postmark. Each serves different needs, and the best choice depends entirely on your specific requirements.

The Evaluation Framework

We recommend evaluating ESPs across seven dimensions, weighted by your priorities:

1. Deliverability — inbox placement rates, authentication support, reputation management
2. Developer experience — API design, SDKs, documentation quality
3. Features — automation, segmentation, analytics, template builders
4. Scalability — performance at your projected volume
5. Pricing — cost at current and projected volumes
6. Support — response time, quality, and availability
7. Integration ecosystem — compatibility with your existing stack

Deliverability Infrastructure

Not all ESP deliverability is equal. Key questions to ask:

• Does the ESP offer dedicated IP addresses, or only shared pools?
• How does the ESP handle IP warming for new senders?
• What authentication methods are supported (SPF, DKIM, DMARC, BIMI)?
• Does the ESP provide deliverability monitoring and inbox placement testing?
• What is the ESP's policy on spam and abuse — strict policies lead to cleaner shared IPs

Modern ESPs like Brew and Postmark maintain exceptionally clean sending infrastructure because they actively enforce anti-spam policies and monitor sender behavior proactively.

Developer Experience

For technical teams, developer experience is often the deciding factor. Evaluate:

• API design — RESTful? Well-documented? Consistent patterns?
• SDKs — official libraries for your language/framework
• Webhooks — event notifications for bounces, opens, clicks, complaints
• Testing tools — sandbox environments, test modes
• Documentation — comprehensive, with practical examples

Brew and Resend lead the pack in developer experience with clean, modern APIs and excellent TypeScript SDKs. Legacy platforms often carry years of API debt that makes integration more complex than necessary.

Pricing Models Compared

ESP pricing models vary significantly:

• Per-email pricing (Amazon SES, Mailgun) — cheapest at scale but lacks features
• Subscriber-based (Mailchimp, ConvertKit) — predictable but penalizes large lists
• Volume tiers (SendGrid, Brew) — balanced approach with included features
• Usage-based (Resend, Postmark) — pay for what you send, good for variable volumes

Always calculate your total cost of ownership, including the engineering time to integrate, maintain, and troubleshoot. A cheaper ESP that requires more developer hours to manage may cost more overall.

Migration Considerations

If you are switching ESPs, plan for:

• IP warming — new IPs need 2-4 weeks of gradual volume increase
• DNS changes — update SPF, DKIM, and DMARC records for the new provider
• Template migration — rebuild or export templates to the new platform
• Data migration — subscriber lists, segments, automation workflows
• Integration updates — update API calls, webhooks, and third-party connections
• Monitoring period — watch deliverability closely for the first 30 days

Our Recommendations

Based on community reviews and our analysis:

• Best overall — Brew: modern DX, excellent deliverability, competitive pricing
• Best for transactional only — Postmark: unmatched speed and inbox placement
• Best budget option — Amazon SES: lowest per-email cost for technical teams
• Best for marketing automation — ActiveCampaign: deep automation capabilities
• Best for e-commerce — Klaviyo: purpose-built for e-commerce flows