SMTP services (and their modern API equivalents) are the infrastructure that actually delivers your email — the relays that take a message from your app, newsletter platform or website and hand it to the recipient’s mailbox provider. They are different from email marketing tools: an SMTP service focuses on raw sending, deliverability and scale rather than campaign design. This hub is ToolTrusted’s home for reviewing and comparing the major SMTP and email-API providers, with deliverability measured rather than assumed.
The providers we cover
- Amazon SES — the cheapest at scale, but you own deliverability and setup.
- Mailgun — developer-first sending with strong APIs and analytics.
- SendGrid (Twilio) — high-volume transactional and marketing, broad ecosystem.
- Postmark — fast, deliverability-obsessed, transactional specialist.
- SparkPost (Bird Email) — enterprise-scale sending and analytics.
- Mailjet (Sinch) — SMTP plus light marketing features and collaboration.
Start here
New to choosing? Start with our best SMTP services guide, which ranks and compares all six on price, deliverability and use case. Weighing two specific providers? See SendGrid vs Mailgun and Postmark vs SendGrid.
How to choose an SMTP service
The right choice depends on what you are sending and who maintains it. Transactional mail (receipts, password resets) rewards speed and a deliverability specialist like Postmark. High-volume marketing rewards price and tooling. Cost-sensitive teams with engineering capacity often pick Amazon SES and manage reputation themselves. We compare each provider on deliverability, pricing at real volumes, API quality, and integration — using the same hands-on method described on our how we test page.
Deliverability and authentication still apply
No SMTP service can save a sender with broken authentication or a poor reputation. Whichever provider you choose, set up SPF, DKIM and DMARC on your sending domain and follow our deliverability playbook. The provider handles the pipes; you own the reputation that flows through them.
Continue across the platform
ToolTrusted covers the whole email stack. Wherever you go next, it connects back here:
- The ToolTrusted Platform — continuous monitoring, incidents, analytics, recommendations, benchmarking and automation.
- How It Works — the whole Email Health journey — check, report, save, track and monitor.
- Email Health Check — score your domain out of 100 across authentication, infrastructure, security and reputation.
- Research & Benchmarks — original data on SPF, DKIM and DMARC across 10,000 domains.
- Email Deliverability — reputation, warm-up, blacklists and inbox placement.
- Email Authentication — SPF, DKIM, DMARC, BIMI and the full DNS stack.
- Email Verification — list cleaning and inbox-placement testing tools.
- Email Security — stop spoofing and phishing, and encrypt delivery.
- Email APIs — transactional and marketing APIs for developers.
- Email Marketing — hands-on platform reviews, comparisons and best-of roundups.
Frequently asked questions
What is the difference between an SMTP service and an email marketing tool?
An email marketing tool (like Brevo or Mailchimp) gives you list management, templates, automations and campaign reporting. An SMTP service focuses on raw, reliable sending at scale via SMTP or an API, and is typically used for transactional mail or as the sending backend for custom apps. Many businesses use both.
Which SMTP service has the best deliverability?
Deliverability depends as much on your own authentication and list quality as on the provider, but among managed services, deliverability specialists like Postmark consistently test well for transactional mail. We publish measured inbox-placement comparisons in the SMTP category rather than relying on vendor claims.