- Email APIs at a glance
- Eleven email APIs worth comparing
- Where to start for your project
- What Gmail expects from every sender
- Email APIs versus SMTP relays
- Questions to ask before you choose an email API
- Signs it's time to change how you send app emails
- My plain advice on choosing an email API
- Frequently asked questions
The best email APIs let your website or app send password resets, receipts, alerts and other transactional emails automatically, and get them into the inbox quickly. Some are open source platforms you run yourself, while others are cloud services that scale to huge volumes. Eleven options follow in no particular order.
The emails nobody thinks about are the ones customers notice most when they fail. A password reset that never arrives, or an order confirmation sitting in spam, turns a happy customer into a support ticket within minutes.
The eleven email APIs below are listed alphabetically and in no particular order, and every description comes from the provider's own website, read this week. Before you switch provider, my email deliverability checklist is worth working through.
Email APIs at a glance
I checked the free plan column on each tool's own website, as of Oct 2026. Yes means the site names a free plan, a free version, a free tier or an open source version. Trial only means a time-limited trial. Not stated means the pages I read named neither, even where there's a button inviting you to start for free, so check the vendor's page before you sign up.
| Tool | Type | Good for | Free plan |
|---|---|---|---|
| AhaSend | Transactional email API and SMTP relay | A European host with a free tier | Yes |
| Amazon SES | Email sending service from AWS | High volume on AWS | Trial only |
| Brevo | Transactional email, SMS and WhatsApp service | Email and SMS from one account | Yes |
| Lettermint | European transactional email platform | Keeping email data in Europe | Not stated |
| Mailgun | Transactional email API for developers | Developer-friendly sending at scale | Yes |
| Mailjet | Email API service for developers | A free tier for growing apps | Yes |
| Mailtrap | Email API with testing tools | Testing and sending in one place | Yes |
| Postal | Open source mail delivery platform | Running your own email server | Yes |
| Postmark | Fast, reliable email delivery service | Fast delivery for app emails | Trial only |
| Resend | Email API for developers | Modern developer experience | Not stated |
| SendGrid | Email API and campaigns from Twilio | Email inside the Twilio family | Trial only |
Eleven email APIs worth comparing
AhaSend
Best for: Small SaaS teams who want a dependable transactional email API hosted in Europe, with a free monthly allowance.
Amazon SES
Best for: Developers already on AWS who want a pay-as-you-go email service that scales to very high sending volumes.
Brevo
Best for: Small businesses that want transactional email, SMS and WhatsApp messages from one account, starting with a free account.
Lettermint
Best for: European businesses that want a local provider for transactional emails, newsletters and inbound email processing.
Mailgun
Best for: Engineering teams who want a long-established email API built for developers, plus a small free daily allowance.
Mailjet
Best for: Growing apps that want an email API with a free tier and no contact-based limits as they grow.
Mailtrap
Best for: Developers who want to test emails safely before sending them, then use the same platform for live delivery.
Postal
Best for: Technical teams who want an open source mail delivery platform they can run on their own servers.
Postmark
Best for: SaaS companies that care most about quick, reliable delivery of password resets and receipts, with a free trial first.
Resend
Best for: Coders who build with modern frameworks and want a clean email API with templates written as code.
SendGrid
Best for: Businesses already using Twilio who want an email API and marketing campaigns from the same provider.
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Where to start for your project
- Fast delivery for password resets and receipts: Postmark.
- Very high volume on AWS: Amazon SES.
- Running your own mail server: Postal.
- Keeping email data in Europe: AhaSend or Lettermint.
- Testing emails before they go live: Mailtrap.
What Gmail expects from every sender
Google's Gmail Help says all senders to personal Gmail accounts must set up SPF or DKIM authentication, and that senders of more than 5,000 messages a day must also set up DMARC, along with other requirements.
That's true whichever email API you choose. Your own domain settings decide whether your emails are trusted, so follow your provider's set-up guide for SPF, DKIM and DMARC before you send anything important.
Email APIs versus SMTP relays
An email API is called directly from your code, which makes it easy to send templates, track events and handle bounces automatically. It's the natural choice for modern web apps.
An SMTP relay works with almost any software that can send email, including older systems, plugins and website builders. Many providers offer both, so you can start with SMTP and move to the API later.
Questions to ask before you choose an email API
- Does it separate transactional and marketing email?
- Where is my data stored and processed?
- Can I see logs of every email sent and opened?
- How does it handle bounces and complaints?
- Does it offer an SMTP relay as well as an API?
- Is there a test mode so emails don't reach real customers?
Signs it's time to change how you send app emails
- Customers say reset emails never arrive. Check your logs.
- Receipts land in spam. Fix your authentication.
- You can't see what was sent. Use a provider with logs.
- Newsletters and receipts share one address. Separate them.
Do you make an email API or transactional email service? Tool makers can ask to be considered for a featured place on this list.
My plain advice on choosing an email API
Keep transactional emails and marketing emails apart, ideally on separate sending addresses or subdomains. If a newsletter ever gets spam complaints, you don't want it dragging your password resets and receipts into the junk folder with it.
Then test with real inboxes before you go live: Gmail, Outlook and Apple Mail at least. If messages already struggle to arrive, my guide on why your email might be marked as spam explains the usual reasons.
Frequently asked questions
What is an email API?
An email API is a service your website or app uses to send emails automatically, such as password resets, receipts and notifications.
What's the difference between transactional and marketing email?
Transactional emails are triggered by something a person did, like resetting a password. Marketing emails promote offers and news to a list.
Are there free email APIs?
Several providers offer free tiers or small free allowances, and some are open source. The free plan column above shows what each provider's own site says.
Do I need SPF, DKIM and DMARC?
Yes. Gmail requires SPF or DKIM from all senders and DMARC from senders of more than 5,000 messages a day.
Can I use SMTP instead of an API?
Yes. Many providers offer an SMTP relay as well as an API, which suits plugins and older software.
Why do my app's emails go to spam?
Common reasons include missing authentication, sending from a shared or new domain, and mixing marketing with transactional email.
