Transactional emails are messages sent in response to various triggers, like user signups, password resets, and other app-specific events. You can send transactional emails through your own servers using a protocol called SMTP — that’s Simple Mail Transfer Protocol — but it’s a lot more nuanced than it sounds. Not only do you need to struggle with formatting your emails, but you also need to stick to a multitude of delivery guidelines to avoid landing in the SPAM folder.

The easier alternative is to use a transactional email API, which does the heavy lifting for you by managing email formatting, delivery, and more. If you’ve looked into email APIs before, you’ll know there’s plenty of choices, with more than a dozen respected providers. In this article, we’ll narrow the choice down to just five of the best email APIs — but first, let’s lay out our criteria.

What to Look for in an Email API

When choosing an email API, the most important criterion is deliverability. For starters, you want to be sure that all of your emails will actually get sent, which reflects both API uptime and performance. Secondly, you want as few emails as possible to land in the SPAM folder (this depends on the provider’s delivery practices as well as the content of your messages).

Aside from deliverability, there are a few industry-wide API criteria to look for:

• Speed
• Security
• Ease of use
• Price

Finally, it’s worth mentioning analytics as an optional criterion. However, do remember that we’re looking to send transactional emails — not marketing emails.

Top 5 Transactional Email APIs

With our requirements out of the way, let’s take a look at five of the most competitive email APIs!

SendGrid

SendGrid, now a Twilio-owned company, is the best-known email API, and also the choice of big corporate names like eBay, Uber, Yelp, Spotify, and others. It has a strong reputation for good deliverability and also offers an impressive analytics panel. As a major player in the industry, it takes Developer Experience very seriously, with an intuitive API and clean, concise documentation. The API has a free plan boasting 100 emails per day, forever. Criticisms of SendGrid include its pricey paid plans and poor support for smaller customers.

Pricing Examples:
30,000 emails: $14.95 per month
300,000 emails: $199.95 per month

What a cURL POST request to the Sendgrid Email API looks like

SendInBlue

SendInBlue offers a popular transactional email API that focuses on providing an all-round, affordable solution. This API also includes SMS messaging and various other marketing tools such as website chatboxes. Importantly, email deliverability is highly rated; in addition, the tool suite is easy-to-us and well-documented. You can view their OpenAPI v3 YAML file here. The API’s free plan offers you 300 emails per day. Downsides include high price tags and the inclusion of SendInBlue branding in all emails in the Free and Lite plans.

Pricing Examples:
30,000 emails: $25 per month
300,000 emails: $173 per month

What cURL POST request to the SendInBlue API looks like

Postmark

Postmark provides an email API that prides itself on delivery speed, aiming to deliver all emails within 10 seconds. Unlike the solutions mentioned previously, this API only offers support for transactional emails — not marketing emails. Postmark claims this results in higher engagement when compared to other email API providers. The API has great documentation and aims to be as transparent as possible with all the crucial stats. Unfortunately, the API has no free plan (unless you’re counting their 100-emails-per-month “developer plan”). It only follows that this is another expensive solution.

Pricing Examples:
30,000 emails: $35 per month
300,000 emails: $200 per month

Postmark provides a nice API Explorer to test out all sorts of API calls. This shows what a call to /deliverystatus will return.

SparkPost

SparkPost is the SaaS branch of Message Systems, which delivers more than a third of the web’s mail. This API claims to have the industry’s best deliverability, also boasting real-time metrics, performance alerts, and other analytics. With 99.99% uptime, it’s hard to beat this API on the technical aspects. The API has good Developer Experience, with plenty of client libraries and comprehensive documentation. SparkPost has no free plan, although there is a trial plan of 500 emails per month.

Pricing Examples:
30,000 emails: $20 per month
300,000 emails: $205 per month

Amazon SES

Amazon SES is an incredibly cheap, lightweight email API with reasonable deliverability. An Amazon product, it’s also fast and reliable. However, it’s not the most refined solution: additional functionality (like analytics) is limited, and the API itself is cumbersome and poorly documented. The API has a generous free plan — but only for Amazon EC2 users — allowing you 62,000 emails per month (more than 2,000 per day).

Pricing Examples:
30,000 emails: Free for Amazon EC2 users; otherwise, $3 per month
300,000 emails: $23.8 per month for Amazon EC2 users; otherwise, $30 per month

Amazon SES charges an additional $0.12 fee per gigabyte of attachments. While the other services on this list don’t charge for attachments, they have size limits which will cause your requests to be rejected if exceeded.

Honorable Mentions

Here are some additional APIs we’ve found since we first wrote this list.

InfoBip

InfoBip’s Email API platform provides a scalable infrastructure that allows up to 120,000 emails to be sent per minute with a 99.4% delivery rate. Other features include:

• Data centers around the world (New York, Frankfurt, Mumbai, and Jakarta) to provide steady and reliable work, with a delivery time of two seconds.
• A dedicated team that helps with onboarding and maximizing delivery rates.
• Flexible pricing model: pay for what you send, no hidden costs or subscriptions.

Which Email API Should You Choose?

Whew! That wraps up our list of five of the best APIs for sending transactional emails. If you’re still wondering which of them to choose, that’s because — honestly — they’re all very similar. It’s quite likely that any (and all) of these APIs will meet your requirements, and at comparable price points. However, here are a few suggestions if you need to make a quick decision:

• If you are a corporate customer with a big budget, choose SendGrid.
• If you value high transparency, opt for Postmark.
• If you need plenty of free emails and/or cheap emails, use Amazon SES.
• If you want additional marketing tools, go for SendInBlue.
• If you want optimal deliverability, choose SparkPost.

Final Thoughts

Transactional emails can play an important role in your web application, so it’s right to want to choose the best email API there is. However, the market’s many providers all have pretty similar offerings. We think five of the best choices are SendGrid, Postmark, Amazon SES, SendInBlue, and SparkPost — all offering excellent speed, deliverability, and usability — but the final decision will definitely depend on your exact use case.