Question 1

What is the best transactional email service?

Accepted Answer

There is no single best transactional email service for every team, but Resend carries the highest review rating (4.8 / 5) among the 12 providers compared here. The right pick depends on volume, budget, and compliance needs, so use the table above to weigh starting price, free tier, and rating, and the "what each provider is best for" section to match a provider to your use case.

Question 2

Which transactional email API has a free tier?

Accepted Answer

Several providers offer an ongoing free tier, including Resend, OneSignal Email, Postmark, Brevo, Loops, AWS SES, Mailgun, SparkPost, and Mailjet. Free allowances and limits vary by provider and change often, and some vendors offer a time-limited trial rather than a perpetual free tier, so check the "Free tier" column above and confirm the current limit on the provider's pricing page.

Question 3

How much does transactional email cost?

Accepted Answer

Pricing is usage-based and scales with send volume. Entry plans in this roundup range from pay-as-you-go sending to fixed monthly plans, as shown in the "Starting price" column. Costs rise with volume, dedicated numbers or IPs, and higher support tiers, so estimate against your real sending volume rather than the headline entry price.

Question 4

What is the difference between transactional and marketing email?

Accepted Answer

Transactional email is triggered by a user action or system event and sent to one recipient at a time: password resets, receipts, order confirmations, and verification codes. Marketing email is sent in bulk to a list to promote or nurture, and is subject to consent and unsubscribe rules. Transactional providers optimize for deliverability, speed, and API reliability.

Question 5

Can I switch transactional email providers without rewriting my code?

Accepted Answer

Often, yes. Courier sits in front of these providers behind one API, so you integrate once and route through any provider in the table, or fail over between them, without rewriting your sending code each time you switch. That means you are not locked into a single vendor's SDK or deliverability.

Question 6

Do these providers support HIPAA and a BAA?

Accepted Answer

Some do. Among the providers compared here, OneSignal Email, Customer.io, AWS SES, Mailgun, and Mailjet will sign a Business Associate Agreement (BAA), usually on specific plans. HIPAA support and BAA availability change by plan and over time, so confirm current terms with the provider before sending protected health information. This reflects each provider's public security or compliance pages as of the date noted below the table.

Provider	Known for	Starting price	Free tier	Rating
Resend	developer experience	$20/mo	3,000/mo	4.8	Guide →
OneSignal Email	bundling email with push	$19/mo	10,000/mo	4.7	Guide →
Postmark	transactional deliverability	$15/mo	100/mo	4.6	Guide →
Brevo	all-in-one marketing and CRM	$9/mo	300/day	4.5	Guide →
Loops	modern marketing email for SaaS	$49/mo	4,000/mo	4.5	Guide →
Customer.io	marketing automation	$100/mo	No	4.4	Guide →
AWS SES	low-cost sending at scale	Usage-based	3,000/mo (1st yr)	4.3	Guide →
Mailgun	flexibility and scale	$15/mo	100/day	4.2	Guide →
Mandrill	its Mailchimp integration	$20/mo	No	4.2	Guide →
SendGrid	breadth and enterprise readiness	$19.95/mo	Trial	4.0	Guide →
SparkPost	high-volume deliverability	$15/mo	1,000/mo	4.0	Guide →
Mailjet	collaborative email design	$9/mo	6,000/mo	3.9	Guide →

Top 12 transactional email API providers [2026]

Transactional Email providers compared

What each transactional email provider is best for

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