Disclosure: I have no affiliation with any of the seven companies below. Nobody paid for this post. I've used all seven myself at one point or another, and they all genuinely work well, this ranking is personal preference, not a verdict. Your own stack, budget, and volume will point you somewhere different, and that's fine.
Every app eventually needs to send email: a password reset, a receipt, a "your export is ready" notification. The API you pick for that ends up quietly load-bearing, since it's the thing standing between your code and whether the email lands in an inbox or a spam folder. Here are seven worth knowing, starting with the one I'd reach for on a new project.
1. SMTPfast
SMTPfast is a transactional email API built on top of Amazon SES, which is a smart place to build from: you inherit SES's deliverability infrastructure and sender reputation tooling without dealing with SES's raw API, its sandbox-mode approval process, or its bare-bones console.
What stands out:
- Free tier with no card required: 3,000 emails/month free, forever, and paid plans start at $9/month for 10,000 emails. Pay-as-you-go overflow credits are $0.001 per extra email if you just need a volume spike without changing plans.
- Both REST and SMTP: send through the JSON API, or point an existing SMTP client at SMTPfast's SMTP bridge using your API key as the password. That second option matters more than it sounds, since it means legacy apps or off-the-shelf software (WordPress, a CMS, an old Rails app) can switch providers without a code change.
- Resend-compatible API: migrating from Resend is close to a base-URL-and-key swap, while adding broadcasts, contact forms, and SES-backed deliverability tooling on top.
- Real-time tracing per email: sends, bounces, opens, and webhook deliveries are traced live, not just logged after the fact. Most providers show you a dashboard after something goes wrong; this one is built around watching it happen.
- Built for AI-agent workflows: a hosted MCP server, a full OpenAPI spec, docs in Markdown, and a Claude Skill, so an AI coding agent can read the API and wire up email sending without someone hand-writing the integration.
Where it's newer than the incumbents: it doesn't have a decade of enterprise deliverability case studies behind it the way Postmark or SendGrid do, and its ecosystem of third-party integrations is smaller. For a new project, especially one already leaning on AI tooling to scaffold itself, the combination of a generous free tier, dual REST/SMTP support, and Resend API compatibility makes it the easiest one to just start with.
2. Postmark
Postmark has been doing exactly one thing since 2010: transactional email, done carefully. It enforces a hard separation between transactional and bulk/marketing sending streams (you can't mix them on the same account), which is exactly why its deliverability reputation is as strong as it is. Inbox providers trust Postmark senders because Postmark actively vets who's allowed to send through it.
That focus is also its limit: if you need marketing campaigns, broadcasts, or bulk sends, Postmark will actively push you elsewhere. It knows what it's for and doesn't pretend to be a full marketing suite.
3. Mailgun
Mailgun is the platform that grew up around the email API rather than around a single product. Beyond sending, it bundles Validate (real-time email address validation to strip bad addresses before you waste a send) and Optimize (a deliverability analytics and strategy layer aimed at teams big enough to have an actual email program, not just a transactional pipe).
It's a solid choice if you expect to outgrow "just send the email" and want validation and deliverability tooling bundled under the same account instead of stitched together from three vendors.
4. SendGrid
SendGrid is now folded into Twilio's product lineup, and its pitch is straightforwardly scale: it advertises delivering over 200 billion emails a month across its customer base. It covers both the transactional Email API and marketing campaign tooling in one platform, which makes it a reasonable single vendor if you need both and don't want to run two systems.
The tradeoff is that "does everything" often means "nothing feels as sharp as a tool built for one job," and Twilio's ongoing rebrand of the product means some docs and dashboards are mid-transition right now.
5. Amazon SES
Amazon SES is the infrastructure layer most of this list is quietly built on, including SMTPfast. Used directly, it's the cheapest way to send email at volume, by a wide margin, but you pay for that price with the experience: a sandbox mode that requires requesting production access before you can send to unverified addresses, a console built for AWS engineers rather than app developers, and no built-in bounce/open dashboard unless you wire one up yourself through SNS and CloudWatch.
The right call if you already live in AWS and are comfortable building the observability layer yourself. The wrong call if you want to be sending your first email within five minutes.
6. Resend
Resend is built specifically for developers shipping from JavaScript/TypeScript stacks, and its biggest differentiator is React Email: you write your email templates as React components instead of hand-rolled HTML strings, and Resend renders and sends them. If your team already thinks in components, this removes an entire category of "why does this email look broken in Outlook" debugging.
It's genuinely good at developer experience, clean SDKs, sensible defaults, fast setup, but it's also young enough that its deliverability track record is shorter than the older players above. Worth it if your stack is already React/Next.js-shaped.
7. SparkPost (now Bird)
SparkPost rebranded to Bird and folded its email product into a broader messaging platform that also covers SMS and other channels. If you've seen "SparkPost" referenced in older tutorials or a colleague's Terraform config, know that the product now lives under Bird's branding, with pricing calculated per 1,000 emails sent. It's aimed at teams building with React or Node who want delivery events and analytics baked in from the start, and it's worth checking whether the migration folded in the deliverability tooling SparkPost was known for, since a rebrand like this is exactly the kind of change that's easy to miss until a doc link 404s on you.
Where that leaves you
If you're starting a new project today and want the least friction between "sign up" and "email delivered," SMTPfast's free tier, SMTP compatibility, and Resend-shaped API make it the one I'd point a new project at first. If you're already deep in React Email templates, Resend is the more natural fit. If deliverability reputation is the whole game (invoices, password resets, anything where a spam-folder miss is a real problem), Postmark's transactional-only discipline is hard to beat. And if you're at the volume where email is its own line item in the budget, Mailgun, SendGrid, or raw SES are where that conversation actually happens.
Pricing and free-tier limits above are as published on each provider's site as of September 2026, worth double-checking before you commit since these numbers move.
