If your application needs to send transactional emails, you'll need a transactional email provider to deliver those emails on your behalf. In this article, we evaluate our favorite seven transactional email service providers you can use as a developer in 2023.

Let's get to it.

The 7 best transactional email APIs for developers

• SendGrid. An industry-leading email API with good deliverability and a comprehensive suite of analytics.
• Postmark. Fantastic deliverability, a well-designed API, and a cost-effective solution for ensuring that your transactional messages get to your customers.
• AWS SES. A highly reliable and scalable option for those who are already within the AWS ecosystem.
• Mailgun. A developer-focused, scalable, and reliable email sending service.
• Resend. Great for developers looking to build and send transactional emails with React or Next.
• MailChimp Transactional (formerly Mandrill). Sold as a paid Mailchimp add-on. If you're already a user of Mailchimp to send marketing announcements, this is a good option.
• Sparkpost. Good deliverability and a robust set of analytics tools make this a solid choice.

Why you should trust us

We're Knock and we're a developer tool for building production-grade, cross-channel notification systems.

We've built integrations with 20+ different notification providers, spent hundreds of hours working with (and discovering the intricacies of) their APIs, and seen up-close how they perform at scale across a wide range of use cases. Today Knock powers production notifications for Vercel, Teikametrics, and SafetyCulture.

What makes a great transactional email service?

• Pricing and value. Cost matters. You want to ensure there's a free tier you can use to "kick the tires" of the service, and understand how the pricing scales as you start sending larger volumes of emails.
• Deliverability. You're using a transactional email service so you don't have to think about deliverability. It's paramount that the transactional email service you use has high deliverability and gets emails to your customer's inbox in a timely fashion.
• Ease of use. Integrating the service into your product should not be a burden, there should be simple instructions and a sane, easy-to-understand set up process to send your first email with the service.
• Documentation and SDKs. As developer-focused services, these providers must have well-designed API and SDKs available in most major languages. Great documentation is also essential, helping you get the support and guidance you need if you get stuck during setup.
• Analytics. Emails generate "exhaust data" for engagement data such as opens and clicks, as well as deliverability data. The service should easily give access to this data, and ideally, make it accessible via a dashboard.

We take an in-depth look at seven transactional email services using the above criteria as a guide to determine how the services stack up against each other. We've created an account on each service, set up a domain, and triggered emails to be sent to see how each service really performs.

As an aside, we used Knock here as a way to quickly integrate the transactional email service, build an email template, and send a test email through each service, without needing to write service-specific integration code. Knock can also take care of managing our email templates, giving us cross-provider analytics, and sending cross-channel notifications to other in-app and out-of-app channels like push, SMS, and Slack.

SendGrid

SendGrid is a widely-used email service from Twilio used by internet giants such as Uber, Booking.com, and Yelp to send and deliver their transactional emails. SendGrid is an excellent option for teams that want to get started quickly and have an email service that will scale with them over time.

SendGrid features

• Comes with outbound (sending) and inbound (receiving) APIs.
• Supports attachments via easy-to-use, base64 encoded content.
• DKIM, DMARC and SPF supported.
• Support for dedicated IP addresses.
• Email address validation API. Note: this is billed separately from email sends.
• Template management, including a visual template editor and a streamlined version control and approval process.

Pros

• Great documentation and SDK support. SendGrid's documentation is easy to navigate, and the quick start guides make it easy to get integrated quickly. There's also SDKs available for most major languages.
• Rich analytics tools. SendGrid has a full suite of tools for monitoring and reporting on email insights. They also offer programmatic access to this data via their API.
• A focus on deliverability and scale. SendGrid has a number of tools to help with deliverability and makes this a core focus of their product, which includes their recent investment into A.I. powered intelligent delivery.

Cons

• Email sending history is a paid add-on. SendGrid offers an extended email activity history add-on that grants access to 30 days of sending history, as well as API access.

SendGrid pricing

SendGrid offers 4 tiers of pricing: Free, Essentials, Pro, and Premier. The free plan offers 100 emails/day, while the Essentials plan starts at $19.95/month and includes 50,0000 emails each month with overages charged on top. Dedicated IP addresses email validations are available in the Pro plan and above. Volume based discounts are available on the Premier plan.

Postmark

Postmark is a transactional email service from ActiveCampaign that prides itself on its inbox deliverability. Compared to some of the offerings in this post, Postmark has a smaller set of customers but is still trusted to power emails for 1Password, Paddle, and Webflow. If you're looking for a no-nonsense service that focuses on deliverability, Postmark is an excellent choice.

Postmark features

• Comes with outbound (sending) and inbound (receiving) APIs.
• Supports attachments via easy-to-use, base64 encoded content.
• DKIM, DMARC and SPF supported.
• Support for dedicated IP addresses.
• 45-day message and log retention on all plans.
• Offers a paid DMARC monitoring service that you can use to track your email sending reputation and proactively address any issues ($10/domain/month).
• Support for webhooks for receiving and processing engagement and delivery events to synchronize with your system.

Postmark also offers a comprehensive dashboard that you can use to look at message-sending and engagement analytics data, as well as creating and maintaining email templates.

Pros

• Deliverability. Postmark consistently has excellent inbox deliverability when compared to some of the other major providers referenced in this post. They relentlessly focus on having great deliverability for transactional emails, and run separate infrastructure for any bulk campaign messages to ensure your transactional emails get to your users' inboxes in a timely manner.
• Visibility into time-to-inbox data. Postmark publish data on time-to-inbox, a metric that's tracked and aggregated across major email providers to document the time between sending an email and it being available within a user's inbox (i.e. delivered).
• Great documentation and SDKs for all major languages. As a developer-focused tool, Postmark has a fantastic set of API documentation and guides, as well as a wide range of official and community-supported SDKs available for all major languages.

Cons

• Lack luster templating. While Postmark does support some templating within their product, the offering is less robust than some of the other services listed in this post (notably SendGrid and SparkPost) given they don't offer a visual, drag-and-drop editor.

Postmark pricing

Postmark offers a simple tiered-volume pricing that's billed monthly. Each plan tier includes a base amount of emails per month, and overages are charged by the thousand at a sliding scale depending on the volume sent. There's also a free developer plan that provides 100 test emails every month for free if you want to try out the service.

Dedicated IP addresses are available for customers sending over 300,000+ emails a month for $50/month.

AWS Simple Email Service (SES)

AWS Simple Email Service (SES) touts itself as "a cost-effective, flexible, and scalable email service". It's a product offering from Amazon Web Services and is designed to send high volumes of transactional emails. AWS SES is lighter on features than some of the other services we're comparing in this list, but if you're already deployed within AWS or use any other products within the AWS suite it might be worth considering as an option.

AWS SES Features

• Inbound (receiving) and outbound (sending) are supported via the API and SDKs.
• Attachments are supported via the raw email sending API.
• Options for static IPs including shared, bring your own, and dedicated IP addresses.
• DKIM, DMARC and SPF supported.
• Tight integration with other AWS services such as EventBridge and Cloudwatch.
• Support for tracking deliverability metrics such as bounces, complaints, and delivery rates.

Pros

• Deliverability at an enormous scale. SES sends hundreds of billions of emails a year for some of the largest internet companies on earth, such as Netflix, Reddit, and Amazon.
• SDKs in all major languages. The AWS SDK is available in all major server-side languages along with thorough accompanying documentation.

Cons

• Setup is complex. As is the case with many AWS services, getting started with SES can be daunting. The documentation and examples often leave a lot to be desired, with auto-generated SDKs and docs making it difficult to understand exactly how the API works.
• All accounts are initially sandboxed. This limits initial sending to 200 messages in a 24-hour period, with restrictions on who can be sent an email (allow listed domains and email addresses). The sandbox restriction can be removed from the SES console.
• Accessing analytics data is non-trivial. To access analytics data (opens, link clicks, deliverability metrics) you need to add an SNS topic to route all events through and then have a destination (like a lambda function) to process the event.

AWS SES pricing

AWS SES is one of the cheapest options for sending emails out there. If your application is already hosted in AWS, then the first 62,000 emails sent each month is free. Beyond that volume emails are priced at $0.10 for every 1,000 emails sent and $0.12 for each GB of attachment data. On the inbound side, the first 1,000 emails are free and then it's $0.10/per 1,000 emails received.

As an aside, it's important to note that with SES, like most AWS services, you will pay for outgoing data and transfer fees:

“You pay for outgoing mail data, incoming mail chunks, and EC2 data transfer fees—even if your usage of Amazon SES qualifies for the AWS Free Usage Tier.“

Pricing with SES can get complicated, so it's probably best if you use the AWS SES pricing calculator to understand exactly how much the service will cost you.

Mailgun

Mailgun from Sinch is a well-established, developer-focused email service that's been in business since 2010. It powers email delivery for some large, well-known companies including Lyft, American Express, and Wikipedia. As a developer-focused tool, Mailgun is fast to get started with and integrate into your product. It's an excellent offering if you're looking for a reliable, easy-to-use product.

Mailgun features

• Comes with outbound (sending) and inbound (receiving) APIs.
• Supports attachments via easy-to-use, base64 encoded content.
• DKIM, DMARC and SPF supported.
• Support for dedicated IP addresses and dedicated IP address pools on higher tiers of sending.
• Has advanced features such as send time optimization.
• Both EU and US-specific sending regions.
• Email address verification tools. Note: these are charged separately from your email sends.
• Support for webhooks for receiving and processing engagement and delivery events to synchronize with your system.

Additionally, Mailgun also comes with a dashboard that you can use to look at emails sent and analytics around engagement and delivery data. The dashboard also allows you to create and maintain email templates using the visual email editor available via Mailjet.

Pros

• Excellent documentation. As a developer-focused offering, Mailgun has a very well-written set of documentation and guides.
• Robust support for deliverability. Mailgun prides itself on its commitment to deliverability with services to pair you with an email expert to ensure you're achieving exceptional deliverability. There's even a great section in their documentation for email best practices for deliverability and sending health.

Cons

• Lack of SDK support. Mailgun has SDKs available in most major languages but has some notable exceptions for their official SDKs including Python, Node, and Elixir.

Mailgun pricing

Mailgun comes with a generous trial tier that includes 5,000 emails included for the first 30 days. Extra sending volume is purchased in blocks of $1.00 per 1,000 messages. There are also paid tiers available that include a base amount of usage each month, with overages charged beyond the base amount. You can learn more and estimate your usage on their pricing page.

All Mailgun plans include 99.99% uptime, 24/7 support, and analytics.

Resend

Resend is a new transactional email service that was in the W23 batch of Y Combinator. As a relatively new player in the email API space, the feature set offered is limited but the (excellent) team at Resend are shipping new features each week to build out the service.

Resend features

• Outbound sending only (no inbound parsing, yet).
• Attachments via easy-to-use, base64 encoded content.
• Support for dedicated IP addresses via an add-on.
• DKIM and SPF supported.
• Created and maintain react email, a transactional email building framework for React.

Resend also comes with a dashboard that you can use to configure the service, view some statistics about the number of messages sent, see API logs for inbound requests, and logs of messages generated.

Pros

• Beautiful documentation and guides. The Resend documentation is well-made, easy to follow, and showcases the team's attention to detail with all things developer experience.
• Deep integration with React. If you're looking to write transactional email templates in React, there's no easier way to send those emails than with Resend's JavaScript SDK.

Cons

• No templating support. Unlike a lot of the other email services in this list, there's no option in Resend to manage templates inside of the dashboard and reference them from the API. This might not be a deal-breaker however, as long as you're comfortable maintaining your templates in your codebase.

Resend pricing

Resend offer 3 pricing tiers: Free, Pro, and Enterprise. The free tier comes with 100 emails a month which must be sent from a verified sender. The pro tier offers a usage based plan, where 50,000 emails is $20/month. Each plan comes with different lengths of data retention for sent messages and logs. The Pro plan can be upgraded with a dedicated IP for $30/month, while the Enterprise plan comes with dedicated IPs out-of-the-box.

Mailchimp Transactional Email (formerly known as Mandrill)

Mailchimp Transactional Email is an email service that's an add-on to the ever popular marketing tool, Mailchimp. It used to be called Mandrill, but in recent years has moved from a standalone service offering to a paid add-on where you must have an existing Mailchimp subscription and plan to use the service. As such, it's an ideal offering if you're an existing Mailchimp customer.

Mailchimp Transactional features

• Comes with outbound (sending) and inbound (receiving) APIs.
• Supports attachments via easy-to-use, base64 encoded content.
• DKIM, DMARC and SPF supported.
• Support for dedicated IP addresses.
• An advanced rules engine to apply rules to inbound or outbound emails.
• Webhooks for email events, so you can respond to engagement and delivery events in real-time from your system.

Pros

• Excellent documentation. Mailchimp has some of the friendliest and best laid out developer documentation out there, making it really easy to get up-and-running and find answers to any questions about the service.
• Strong focus on deliverability and speed of delivery. Mailchimp has a set of global infrastructure that's employed to deliver emails quickly, while ensuring great deliverability. There's also support for IP address warming, dedicated IP addresses, and IP address pools.
• Solid analytics and reporting capabilities. The dashboard has the ability to pull reports on deliverability, opens, clicks, bounces, and rejections. There are also logs that can be searched for outgoing messages by tags and subject lines.

Cons

• Requires an existing Mailchimp subscription. As mentioned above, Mailchimp transactional requires an existing Mailchimp Standard or Premium subscription in order to purchase the add on and start sending transactional messages.

Mailchimp Transactional pricing

Mailchimp's Transactional pricing is based around the concept of blocks, where each block is a credit for 25,000 emails. Blocks are charged on a sliding scale, where the more blocks that are purchased the lower the cost per block. For example, to send 100,000 emails a month the cost will be $80. In addition, there's also a free plan available to new transactional email users with 500 free email sends included to a verified domain, and you can purchase a dedicated IPs for $29.95/month.

Please note: you will need a Mailchimp account on the Standard or Premium plan to use Mailchimp Transactional Emails.

SparkPost

SparkPost is an enterprise-grade email service from MessageBird that sends 37% of all emails for B2B and B2C applications. It's used by Twitter, Pinterest, and Zillow to reliably send and deliver emails. Although SparkPost is an enterprise-grade service, it's also accessible to teams at all sizes and prices very competitively.

SparkPost features

• Comes with outbound (sending) and inbound (receiving) APIs.
• Supports attachments via easy-to-use, base64 encoded content.
• DKIM, DMARC and SPF supported.
• Dedicated IP addresses, IP address pools, and IP address warming.
• Support for webhooks for receiving and processing engagement and delivery events to synchronize with your system (note: there are a limited number of available webhooks on the starter and premier plans).

Pros

• Support for subaccounts. If you have multiple applications that need isolated sending streams, but you want to bill them under a single consolidated account, then SparkPost's subaccounts are a useful feature.
• On-premise mail sender. SparkPost is the only provider that offers an on-premise mail sending solution for very high volume workloads.
• Great analytics tools. SparkPost includes a whole host of analytics tools to understand delivery rates, including a predictive health score for your emails.
• Excellent template management tools. There are a whole suite of template management tools built into SparkPost.

Cons

• Hard-to-navigate documentation. While SparkPost has pretty comprehensive documentation, it's not always easy to navigate around find the specific answers your looking for. The getting started guides are also less comprehensive and beginner-friendly than some of the other services mentioned in this article.

SparkPost pricing

SparkPost offer 3 tiers of pricing: Starter, Premier, and Enterprise. There's also a free developer trial available that can be used to try out features before signing up for a paid plan. The Premier and Enterprise plans are available when your monthly volume exceeds 100,000 emails/month, with both including a Dedicated IP address as part of the plan. For much higher volumes, an Enterprise plan is available.

Using Knock to build a transactional notification system

Adding transactional email support to your product is usually one of the first steps to building out more notifications from your product, but before long you may find yourself in the weeds building lots of different types of notifications across disparate channels. This is where Knock can help.

Knock is a developer tool for building cross-channel notification systems. With Knock, you can create complex cross-channel notifications for your product without writing complex notification code yourself. You call Knock's API and you can send notifications to in-app and out-of-app channels such as email, push, SMS, and Slack.

Even if you're only planning on sending emails from your product, Knock can help. You can use Knock's dashboard to collaboratively manage your email templates, either with a drag-and-drop visual builder or by dropping down to writing HTML. Knock also takes care of all of your retry and delivery logic, as well as batching (collapsing multiple notifications about a single topic into one), managing per-user notification preferences, and providing unparalleled visibility into the notifications your product is sending.

If you'd like to try it out, you can sign up for a free account or chat with our team. 👋