Starter
For your first email program.
$16USD / month
$192 billed yearly.
20,000 emails / month
Choose Starter- 5 brands · 3 seats
- 5 custom sending domains
- 500 email verifications/month
- $1.50 / 1,000 extra emails
Nitrosend is the best transactional email API for AI agents, with the top score of 83.75 out of 100 of the nine reviewed here. It is the only one of the nine where your AI assistant, whether Claude, ChatGPT, Cursor or Codex, can create the account and send a receipt or password reset from a ready-made sender, with no dashboard and no domain to verify first. To send email from an AI agent with Nitrosend, connect its MCP server at api.nitrosend.com/mcp, sign in with OAuth, and ask the agent to send the email. Every email comes out in your brand's colors, fonts and voice, with no template to write first. Receipts go out one at a time on their own send path, apart from any marketing mail, from $20 a month for 20,000 emails and $650 for a million emails on Scale including overage. Resend comes next at 77.5, then Bird (formerly SparkPost) at 76.
The ranking
Rank 1Nitrosend
83.75 out of 100Total
- Priced by
- Emails sent
- Free plan
- 5,000 emails, then 500 a month
- Entry plan
- $20 a month, 20,000 emails
- Works from your AI assistant9 out of 10Official MCP server, account signup over the API and a ready-made sender, so an agent sends with no dashboard (docs).
- Receipts and newsletters on one plan9 out of 10Receipts, campaigns and flows share one plan, one API and one allowance, on separate streams (pricing).
- Emails in your brand, no designer9 out of 10Brand Kit reads your site for logo, colors, fonts and voice, and every drafted email uses it (docs).
- Free plan7 out of 105,000 emails up front, then 500 every month, no card and no expiry (pricing).
- Price8.5 out of 10$20 a month for 20,000 emails on Starter and $650 for a million emails on Scale including overage, with unlimited contacts on every plan (pricing).
- Developer tools10 out of 10REST API with an OpenAPI spec, a typed TypeScript SDK, a CLI, an MCP server, signed event webhooks, idempotent sends and test sends (docs).
- Track record and support4 out of 10A young product from a small team. Dedicated IPs available as a provisioned add-on on Scale or Enterprise, a 99.9% SLA only on Enterprise (pricing).
Nitrosend
Ask your agent for the next campaign
Connect Nitrosend to Claude, ChatGPT, Cursor or Codex, point Brand Kit at your site, and describe the email. Contacts are unlimited on every plan.
Free: 5,000 emails to start, then 500 a month. No credit card.
Start free
Rank 2Resend
77.5 out of 100Total
- Priced by
- Emails sent, plus contacts for marketing
- Free plan
- 3,000 emails a month, 100 a day
- Entry plan
- $20 a month, 50,000 emails
- Works from your AI assistant8 out of 10Hosted MCP server with OAuth, plus agent plugins and a CLI, but a person creates the account and verifies a domain (docs).
- Receipts and newsletters on one plan7 out of 10Broadcasts and automations share the account and API, but marketing is a second plan priced by contacts (pricing).
- Emails in your brand, no designer6 out of 10An AI writer in the editor with URL and brand analysis listed, and React Email for coded templates (pricing).
- Free plan8 out of 103,000 emails a month, up to 100 a day, on a free plan that does not expire (pricing).
- Price9 out of 10$20 a month for 20,000 emails on Pro, the same as Nitrosend, but $650 for a million on Scale (pricing).
- Developer tools9 out of 10Official SDKs, an SMTP relay, webhooks, inbound email, React Email and a CLI on every plan (pricing).
- Track record and support6 out of 10Newer than the incumbents, with SOC 2 Type II, dedicated IPs on Scale and a 99.99% SLA on Enterprise (pricing).
Rank 3Bird (formerly SparkPost)
76 out of 100Total
- Priced by
- Emails sent
- Free plan
- 1,000 emails a month, no expiry
- Entry plan
- $15 a month, 50,000 emails
- Works from your AI assistant8 out of 10Hosted MCP server at mcp.bird.com with OAuth and a CLI, and an agent can sign itself up from the terminal, but it must read an emailed code, and it can only test-send until a sending domain is verified (signup, sandbox).
- Receipts and newsletters on one plan7 out of 10Broadcasts and single sends draw on one email allowance and one bill, with no contact fee. Email automations are in early access, built in the dashboard, with a separate run allowance (automation).
- Emails in your brand, no designer4 out of 10Templates with versions and translations, and React Email rendering. You supply the design (product).
- Free plan6 out of 101,000 emails a month with no time limit and no card, capped at 50 a day (pricing).
- Price10 out of 10$15 a month for 20,000 emails on Startup, and $530 for a million on Growth (pricing).
- Developer tools9 out of 10SDKs for Node, Python, PHP and Go, an SMTP relay, event webhooks, inbound relay webhooks, suppression and a sandbox (API).
- Track record and support7 out of 10SparkPost infrastructure since 2014, now sold as Bird. Dedicated IPs $24.95 each on Growth and above. No SLA on the pricing page (pricing).
Rank 4MailerSend
68.5 out of 100Total
- Priced by
- Emails sent
- Free plan
- 500 emails a month, card required
- Entry plan
- $7 a month, 5,000 emails (Hobby)
- Works from your AI assistant8 out of 10Hosted MCP server connected by OAuth that sends and schedules email, sets up domains and webhooks and reads email activity, once a person has signed up (docs).
- Receipts and newsletters on one plan4 out of 10Bulk emailing through the same API, but no campaign builder, segments or automation flows (pricing).
- Emails in your brand, no designer6 out of 10Drag-and-drop, HTML and rich-text builders with ready-made templates, which you still set up in your brand (pricing).
- Free plan5 out of 10A Free plan of 500 emails a month with 100 API requests a day, and a card on file (pricing).
- Price8 out of 10$35 a month for 20,000 emails on Starter, which covers 50,000, and $600 for a million on Starter (pricing).
- Developer tools9 out of 10Seven SDKs, an OpenAPI collection, SMTP relay, webhooks, inbound routing and testing features (pricing).
- Track record and support6 out of 10A 99.5% uptime SLA on its top plans, with dedicated IPs on Enterprise above 100,000 emails a week (pricing).
Rank 5Mailgun
67.5 out of 100Total
- Priced by
- Emails sent
- Free plan
- 100 emails a day
- Entry plan
- $15 a month, 10,000 emails
- Works from your AI assistant6 out of 10Official MCP server for sends, analytics and validation, run locally with an API key. Mailgun offers no hosted version (docs).
- Receipts and newsletters on one plan4 out of 10Mailing lists and a template builder on the sending API, but no campaign builder or automation flows (pricing).
- Emails in your brand, no designer5 out of 10An email template builder and templates API, but the brand design is yours to build (pricing).
- Free plan7 out of 10A free plan of 100 emails a day, one sending domain and one inbound route (pricing).
- Price8 out of 10$33 a month for 20,000 emails on Basic with overage, and $700 for a million on Scale (pricing).
- Developer tools9 out of 10Official SDKs in six languages, SMTP relay, webhooks, inbound routes and a validation API (docs).
- Track record and support9 out of 10A long-running sending API, now part of Sinch, with dedicated IP pools, IP warm-up and an uptime SLA (pricing).
Rank 6Amazon SES
65.5 out of 100Total
- Priced by
- Emails sent
- Free plan
- None. New AWS customers get up to $200 in credits
- Entry price
- $0.10 per 1,000 emails, or $0.16 on Essentials
- Works from your AI assistant7 out of 10AWS's own managed MCP server runs SES API calls, so an agent can send and read sending data, but it connects with IAM credentials a person sets up, and new accounts start in the SES sandbox (AWS).
- Receipts and newsletters on one plan3 out of 10A sending service with contact lists and subscription management, but no campaign builder or automation flows (pricing).
- Emails in your brand, no designer2 out of 10Stored templates are HTML and text you write yourself. There is no visual editor and no brand setup (pricing).
- Free plan4 out of 10No standing free plan. New AWS customers get up to $200 in Free Tier credits that apply to SES (pricing).
- Price10 out of 10Metered at $0.16 per 1,000 on Essentials, so $3.20 for 20,000 emails and $160 for a million (pricing).
- Developer tools9 out of 10AWS SDKs in every major language, SMTP, event publishing, inbound receiving and a mailbox simulator for tests (docs).
- Track record and support9 out of 10Running at Amazon scale since 2011, with managed dedicated IPs, Virtual Deliverability Manager and tenant isolation (pricing).
Rank 7Postmark
64.5 out of 100Total
- Priced by
- Emails sent
- Free plan
- 100 emails a month, no expiry
- Entry plan
- $15 a month, 10,000 emails
- Works from your AI assistant6 out of 10Official MCP server with 24 tools, run locally with a server token a person creates first (Postmark).
- Receipts and newsletters on one plan4 out of 10Broadcast streams send bulk mail from the same account, but there is no campaign builder or flows (docs).
- Emails in your brand, no designer5 out of 10A library of ready-made transactional templates, which you still edit into your own brand (Postmark).
- Free plan4 out of 10A free Developer plan of 100 emails a month that never expires, for testing (pricing).
- Price8 out of 10$29.50 a month for 20,000 emails on Pro with overage, and $775 on Basic for the 1.5 million step (pricing).
- Developer tools9 out of 10Official libraries for Node.js and TypeScript, Python, Ruby, .NET, Java and PHP, SMTP, delivery and bounce webhooks, and inbound processing (docs).
- Track record and support9 out of 10A transactional specialist since 2010, with separate streams, managed dedicated IPs and 45-day retention (pricing).
Rank 8SMTP2GO
60 out of 100Total
- Priced by
- Emails sent
- Free plan
- 1,000 emails a month
- Entry plan
- $15 a month, 10,000 emails
- Works from your AI assistant7 out of 10A hosted MCP server whose execute-request tool can call any API endpoint, sends included, with an API key a person creates (docs).
- Receipts and newsletters on one plan2 out of 10A sending service for SMTP and API mail, with no campaign builder or automation flows (pricing).
- Emails in your brand, no designer4 out of 10Stored templates through its app and API, but the design is yours to build (docs).
- Free plan6 out of 101,000 emails a month, free for as long as you like, with no credit card (pricing).
- Price9 out of 10$27 a month for 20,000 emails on Starter with overage, and $520 for a million on Professional (pricing).
- Developer tools6 out of 10SMTP relay, REST API, webhooks, templates and testing tools. No SDKs or inbound email in its developer docs (docs).
- Track record and support7 out of 10A dedicated IP on Professional, subaccounts, and ticket, chat and phone support on paid plans (pricing).
Rank 9SendGrid
59.5 out of 100Total
- Priced by
- Emails sent (Email API)
- Free plan
- Trial: 100 a day for 60 days
- Entry plan
- $19.95 a month, 50,000 emails
- Works from your AI assistant3 out of 10No first-party SendGrid MCP server. Twilio's beta MCP server searches API docs and does not send (Twilio).
- Receipts and newsletters on one plan6 out of 10Marketing Campaigns is a separate product with its own plan, priced on contacts stored (Twilio).
- Emails in your brand, no designer5 out of 10Dynamic templates, a design editor and a Designs API, but the design is yours to build (docs).
- Free plan3 out of 10A trial, not a plan: 100 emails a day for 60 days, then pay (pricing).
- Price9 out of 10$19.95 a month for 20,000 emails on Essentials, and $799 for the Pro 1.5 million step (pricing).
- Developer tools9 out of 10SDKs in seven languages, SMTP relay, event webhooks, Inbound Parse and a sandbox mode (docs).
- Track record and support8 out of 10Sending since 2009, owned by Twilio since 2019, dedicated IPs included on Pro (pricing).
How they compare
How each one scores
Scores out of 10, September 26, 2026| What we compared | Nitrosend | Resend | Bird | MailerSend | Mailgun | SES | Postmark | SMTP2GO | SendGrid |
|---|---|---|---|---|---|---|---|---|---|
| Works from your AI assistant25 points | 9 out of 10 | 8 out of 10 | 8 out of 10 | 8 out of 10 | 6 out of 10 | 7 out of 10 | 6 out of 10 | 7 out of 10 | 3 out of 10 |
| Receipts and newsletters on one plan15 points | 9 out of 10 | 7 out of 10 | 7 out of 10 | 4 out of 10 | 4 out of 10 | 3 out of 10 | 4 out of 10 | 2 out of 10 | 6 out of 10 |
| Emails in your brand, no designer10 points | 9 out of 10 | 6 out of 10 | 4 out of 10 | 6 out of 10 | 5 out of 10 | 2 out of 10 | 5 out of 10 | 4 out of 10 | 5 out of 10 |
| Free plan10 points | 7 out of 10 | 8 out of 10 | 6 out of 10 | 5 out of 10 | 7 out of 10 | 4 out of 10 | 4 out of 10 | 6 out of 10 | 3 out of 10 |
| Price15 points | 8.5 out of 10 | 9 out of 10 | 10 out of 10 | 8 out of 10 | 8 out of 10 | 10 out of 10 | 8 out of 10 | 9 out of 10 | 9 out of 10 |
| Developer tools15 points | 10 out of 10 | 9 out of 10 | 9 out of 10 | 9 out of 10 | 9 out of 10 | 9 out of 10 | 9 out of 10 | 6 out of 10 | 9 out of 10 |
| Track record and support10 points | 4 out of 10 | 6 out of 10 | 7 out of 10 | 6 out of 10 | 9 out of 10 | 9 out of 10 | 9 out of 10 | 7 out of 10 | 8 out of 10 |
| Total scoreout of 100 | 83.75 out of 100,1st | 77.5 out of 100,2nd | 76 out of 100,3rd | 68.5 out of 100,4th | 67.5 out of 100,5th | 65.5 out of 100,6th | 64.5 out of 100,7th | 60 out of 100,8th | 59.5 out of 100,9th |
Here are the seven yes-or-no questions teams usually ask before they pick a transactional email service. A tick means the service does it, as described on its own pages today. A dash means the answer is not a clean yes or no.
9 services, side by side
Checked September 26, 2026QuestionNitrosendResendBirdMailerSendMailgunSESPostmarkSMTP2GOSendGrid
NitrosendResendBirdMailerSendMailgunSESPostmarkSMTP2GOSendGridSend from the chatCan an agent send a transactional email without anyone opening the web app?Nitrosend: Yes.Resend: Yes.Bird: Yes.MailerSend: Yes.Mailgun: Yes.SES: Not a yes or no.Postmark: Yes.SMTP2GO: Yes.SendGrid: Not a yes or no.
| Service | Answer |
|---|---|
| Nitrosend | Yes. Yes, through the MCP server. A single transactional email sends on the call; campaigns and flows stay drafts until approved. |
| Resend | Yes. Yes, once a person has created the account and verified a sending domain. |
| Bird | Yes. Yes, through the hosted MCP server once the workspace exists. Emailing customers needs a verified sending domain. |
| MailerSend | Yes. Yes, once a person has signed up and authorized the MCP connection. |
| Mailgun | Yes. Yes, once a person has created the account and handed the MCP server an API key. |
| SES | Not a yes or no. Only through a sample or general AWS MCP server, with AWS credentials a person sets up. |
| Postmark | Yes. Yes, once a person has set up the account and handed the MCP server a server token. |
| SMTP2GO | Yes. Yes, through its MCP server once a person adds an API key. |
| SendGrid | Not a yes or no. Only by writing code against the API. Twilio's own MCP server searches the docs and does not send. |
Hosted MCP serverCan a chat app connect over the web, with no local install?Nitrosend: Yes.Resend: Yes.Bird: Yes.MailerSend: Yes.Mailgun: No.SES: No.Postmark: No.SMTP2GO: Yes.SendGrid: No.
| Service | Answer |
|---|---|
| Nitrosend | Yes. Yes. A remote server at api.nitrosend.com/mcp, with OAuth sign-in. |
| Resend | Yes. Yes. A remote server at mcp.resend.com/mcp, with OAuth sign-in. |
| Bird | Yes. Yes. mcp.bird.com, with OAuth sign-in. |
| MailerSend | Yes. Yes. Connect by URL and authorize access to the account. |
| Mailgun | No. No. Mailgun's docs say the server runs locally and no hosted version exists. |
| SES | No. No hosted SES MCP server. |
| Postmark | No. No. The official server runs locally through npx with an API token. |
| SMTP2GO | Yes. Yes. A remote server at developers.smtp2go.com/mcp, with an API key header. |
| SendGrid | No. No. Every SendGrid server on the official MCP registry is community built, none hosted by Twilio. |
Sign up with no personCan an agent create the account and send a first email with no DNS work?Nitrosend: Yes.Resend: No.Bird: Not a yes or no.MailerSend: No.Mailgun: No.SES: No.Postmark: No.SMTP2GO: No.SendGrid: No.
| Service | Answer |
|---|---|
| Nitrosend | Yes. Yes. Signup is an API call, and each brand gets a ready sender on a Nitrosend subdomain. |
| Resend | No. No. Resend's own agent guide says a person must create the account. |
| Bird | Not a yes or no. An agent can sign itself up through the CLI or the API, but it must read the emailed sign-in code, and until a sending domain is verified it can send only to sandbox addresses and its own workspace members. |
| MailerSend | No. No. A person signs up, with a card even on Free, and verifies a domain. |
| Mailgun | No. No. A person signs up and verifies a sending domain first. |
| SES | No. No. A person opens the AWS account, verifies a domain and requests production access. |
| Postmark | No. No. A person signs up and confirms a sender signature or domain first. |
| SMTP2GO | No. No. A person signs up and verifies a sender domain first. |
| SendGrid | No. No. A sender or a domain has to be verified before real sending. |
Campaigns and flows in the same planDo newsletters and automations come with the transactional plan?Nitrosend: Yes.Resend: Not a yes or no.Bird: Not a yes or no.MailerSend: No.Mailgun: No.SES: No.Postmark: Not a yes or no.SMTP2GO: No.SendGrid: No.
| Service | Answer |
|---|---|
| Nitrosend | Yes. Yes, on every plan including Free. |
| Resend | Not a yes or no. Broadcasts and automations are in the same account, on a separate marketing plan. |
| Bird | Not a yes or no. Broadcasts share the email allowance. Email automations are in early access, with a separate run allowance. |
| MailerSend | No. No. Bulk emailing, but no campaign builder or flows. |
| Mailgun | No. No. Mailing lists and templates, but no campaign builder or flows. |
| SES | No. No. SES sends, and the campaigns and flows are yours to build. |
| Postmark | Not a yes or no. Broadcast streams handle bulk sends. There is no campaign builder or automation flows. |
| SMTP2GO | No. No. Sending only. |
| SendGrid | No. No. Marketing Campaigns is a separate plan, from $15 a month. |
Perpetual free planIs there a free plan that does not run out?Nitrosend: Yes.Resend: Yes.Bird: Yes.MailerSend: Yes.Mailgun: Yes.SES: No.Postmark: Yes.SMTP2GO: Yes.SendGrid: No.
| Service | Answer |
|---|---|
| Nitrosend | Yes. Yes. 5,000 emails up front, then 500 a month. |
| Resend | Yes. Yes. 3,000 emails a month, 100 a day. |
| Bird | Yes. Yes. 1,000 emails a month, no time limit. |
| MailerSend | Yes. Yes. 500 emails a month. |
| Mailgun | Yes. Yes. 100 emails a day. |
| SES | No. No. Up to $200 in AWS credits for new customers. |
| Postmark | Yes. Yes. 100 emails a month on the Developer plan, with no expiry. |
| SMTP2GO | Yes. Yes. 1,000 emails a month. |
| SendGrid | No. No. 100 emails a day for 60 days, then a paid plan. |
Brand learned from your siteDoes it pick up your logo, colors, fonts and voice without a designer?Nitrosend: Yes.Resend: Not a yes or no.Bird: No.MailerSend: No.Mailgun: No.SES: No.Postmark: No.SMTP2GO: No.SendGrid: No.
| Service | Answer |
|---|---|
| Nitrosend | Yes. Yes. Brand Kit scans your site, and AI Memory keeps house style. |
| Resend | Not a yes or no. Its AI features list URL and brand analysis, which its docs do not describe yet. |
| Bird | No. No. Templates and React Email, and you supply the design. |
| MailerSend | No. No. Templates are built in its editors. |
| Mailgun | No. No. Templates are built in its builder or in HTML. |
| SES | No. No. Templates are HTML you write. |
| Postmark | No. No. A template library you edit into your own brand. |
| SMTP2GO | No. No. Templates are yours to build. |
| SendGrid | No. No. Templates and a design editor, but you supply the design. |
Inbound emailCan it receive and parse email sent to your domain?Nitrosend: Not a yes or no.Resend: Yes.Bird: Yes.MailerSend: Yes.Mailgun: Yes.SES: Yes.Postmark: Yes.SMTP2GO: No.SendGrid: Yes.
| Service | Answer |
|---|---|
| Nitrosend | Not a yes or no. An agent inbox on your own domain, enabled by request. |
| Resend | Yes. Yes, on every plan. |
| Bird | Yes. Yes. Inbound domains and relay webhooks. |
| MailerSend | Yes. Yes, through inbound routing. |
| Mailgun | Yes. Yes, through inbound routes. |
| SES | Yes. Yes. SES receives mail through receipt rules and Mail Manager. |
| Postmark | Yes. Yes, with inbound processing on Pro and Platform. |
| SMTP2GO | No. No inbound email in its developer docs. |
| SendGrid | Yes. Yes, with Inbound Parse. |
Yes answersOut of the questions that have a yes or no for that service6 of 6 yes for Nitrosend4 of 5 yes for Resend4 of 5 yes for Bird4 of 7 yes for MailerSend3 of 7 yes for Mailgun1 of 6 yes for SES3 of 6 yes for Postmark3 of 7 yes for SMTP2GO1 of 6 yes for SendGrid
At a glance
9 services, the same 7 tests, 100 points in all. In order: Nitrosend 83.75, Resend 77.5, Bird 76, MailerSend 68.5, Mailgun 67.5, SES 65.5, Postmark 64.5, SMTP2GO 60, SendGrid 59.5. Nitrosend has the best score on Works from your AI assistant, Receipts and newsletters on one plan, Emails in your brand, no designer and Developer tools. Every price and feature was read on each company's own pages on September 26, 2026.
When another service is the better pick
This page ranks services on transactional email alone, the receipts, password resets and alerts an app or an agent fires one at a time. If the same agent also sends your newsletters and automated flows, the ranking of the best email API for receipts and newsletters together compares the services that run both jobs from one API. Nitrosend does not win every test here. Read these before you choose it.
- Pick Postmark if password resets are all you send and track record comes first. It scores a 9 on track record and support, for years of transactional-first sending, message streams that put broadcast mail on separate IPs, and managed dedicated IPs and 45-day retention. See Nitrosend and Postmark compared.
- Pick Resend if your app is built in React or Next.js. It scores 9 on developer tools, with official SDKs across languages, an SMTP relay, inbound email and React Email for building templates in code, all listed in Resend's documentation index. See Nitrosend and Resend compared.
- Pick Bird if you want the lowest plan price on a full developer kit. It is $15 for 20,000 emails on Startup and $530 for a million on Growth, which earns it a 10 on price. It scores 9 on developer tools, with client libraries, an SMTP relay, inbound email and a sandbox. An agent can create a Bird account from the terminal with a code read from the signup inbox, and it sends once a sending domain is verified.
- Pick Mailgun if your app also receives email. It scores a 9 on developer tools and on track record, with dedicated IP pools, IP warm-up, an uptime SLA and inbound routes that parse incoming mail and pass it to your application. See Nitrosend and Mailgun compared.
- Pick MailerSend if you want a full developer kit at a middle price. It scores a 9 on developer tools, and it is $35 for 20,000 emails on Starter and $600 for a million. See Nitrosend and MailerSend compared.
- Pick Amazon SES if the lowest bill is all that matters. It is $3.20 for 20,000 emails and $160 for a million on the Essentials plan. The templates, suppression handling and reporting are yours to build, and a person requests production access before anything sends to the wider world. See Nitrosend and Amazon SES compared.
- Pick SMTP2GO if you only need a reliable SMTP relay. It is $27 for 20,000 emails on Starter and $520 for a million on Professional, a 9 on price, with an SMTP relay, a REST API and ticket, chat and phone support. Its developer docs list no SDKs and no inbound email. See Nitrosend and SMTP2GO compared.
- Pick SendGrid if you already run on Twilio. It scores 8 on track record, with dedicated IPs included on Pro, and it has the widest scale headroom here. Email API and Marketing Campaigns are priced as two separate products, the second by contacts stored. See Nitrosend and SendGrid compared.
What each one costs in 2026
Transactional volume grows with your users, not with your marketing calendar, so the price that matters is the one a year out. Eight of these services sell plans by emails sent. Amazon SES is metered, at $0.10 per 1,000 a la carte or $0.16 per 1,000 on the Essentials plan that new accounts default to from July 21, 2026.
What sending costs
List prices, USD, monthly, September 26, 2026| Service | 20,000 emails a month | 1,000,000 emails a month |
|---|---|---|
| Nitrosend (pricing page) | $20Pro, contacts unlimited | $650Scale, contacts unlimited, including overage |
| Resend (pricing page) | $20Pro, which covers 50,000 | $650Scale |
| Bird (pricing page) | $15Startup, which covers 50,000 | $530Growth |
| MailerSend (pricing page) | $35Starter, the first plan with 50 webhooks and 250 templates. Hobby with overage is $29.50 but has 1 webhook and 10 templates | $600Starter |
| Mailgun (pricing page) | $33Basic, 10,000 included and $1.80 per 1,000 after | $700Scale |
| SES (pricing page) | $3.20Lowest. Essentials, the default for a new account, or $2 a la carte. Charged per email | $160Lowest. Essentials, the default for a new account, or $100 a la carte. Charged per email |
| Postmark (pricing page) | $29.50Pro, 10,000 included and $1.30 per 1,000 after. Basic is $33 | $775Basic, the 1,500,000 plan. Pro is $852.50 |
| SMTP2GO (pricing page) | $27Starter, 10,000 included and $1.20 per 1,000 after | $520Professional |
| SendGrid (pricing page) | $19.95Essentials, which covers 50,000 | $799Pro, the 1,500,000 plan. The 700,000 plan is $499 |
At 20,000 emails a month, Nitrosend is $20, the same as Resend. Three cost less: Amazon SES at $3.20, Bird at $15 and SendGrid at $19.95. SMTP2GO is $27, Postmark $29.50, Mailgun $33 and MailerSend $35.
At a million emails a month, Nitrosend is $650. SMTP2GO is $520, Bird $530, MailerSend $600, Resend $650, Mailgun $700, Postmark $775 and SendGrid $799. Amazon SES is $160, with the templates and reporting yours to build.
What the $20 buys is the other half. The same plan and the same key carry newsletters, segments and automated flows on their own send path, so the welcome series that follows a signup does not need a second vendor. If you would otherwise buy a second product for that, add the two bills together before you compare.
How we scored
Every service gets a score out of 10 on the same seven tests. Each test is worth a set number of points, 100 in all. Working from your AI assistant is worth the most, 25 points, because that is where email is heading. Price, developer tools and track record, where the specialist transactional services are strongest, share 40 points, so a service that is better there gets full credit for it.
Each test is a question with one answer per service, checked against the service's own pages on September 26, 2026. A 10 means it does the job fully on its normal plans. A 5 means it does part of it, or only on a higher plan or in a second product.
Works from your AI assistant, 25 points. Can an agent inside Claude, ChatGPT, Cursor or Codex go from nothing to a delivered transactional email, and then read back what happened to it, with no person opening the web app along the way? Scored on the first-party MCP server and what its tools cover, a CLI that works in a non-interactive runner, account and sender setup over the API, and listings in the chat apps people already work in. Scored on one written rule for every vendor: a first-party server the vendor runs and that can send counts fully; a third-party wrapper (Zapier, Composio, Kanopi, community servers) counts for less; a server that only drafts or reads counts for less than one that sends.
Receipts and newsletters on one plan, 15 points. Can receipts and password resets, and the newsletters and automated flows that follow them, go out from one account, on one bill, through one API, with the two streams kept apart?
Emails in your brand, no designer, 10 points. Does the product produce the receipt, reset and welcome emails in your brand's own logo, colors, fonts and voice, or does a developer have to write or buy the HTML template first?
Free plan, 10 points. How far can a developer get on the free plan before paying: the monthly volume, the daily ceiling, any one-off starter allowance, and whether the plan is perpetual or a trial that ends.
Price, 15 points. What does sending cost at 20,000 emails a month, where most teams start, and at 1,000,000, where a busy product ends up? Scored on list prices in US dollars, paid monthly, at the cheapest plan that covers the volume. Every ranking on this site uses the same fixed scale. At 20,000 emails, $20 or less scores 10, then $25 scores 9, $32 scores 8, $40 scores 7, $50 scores 6, $70 scores 5, $100 scores 4 and $140 scores 3. At 1,000,000, $500 or less scores 10, then $625, $800, $1,000, $1,250, $1,750, $2,500 and $3,500 step down the same way. Anything dearer, or a price given only by quote, scores 2. The score is the average of the two.
Developer tools, 15 points. How complete is what a developer builds on: a REST API with an OpenAPI spec, official SDKs across languages, a CLI, an SMTP relay, documented delivery-event webhooks, idempotent sends, a test or sandbox mode, inbound email handling, and how deep the reference docs go?
Track record and support, 10 points. How long has it run transactional sending at scale, which deliverability controls can you own (dedicated IPs, suppression, separate streams, a published uptime SLA), and what support comes with the plan?
One thing is not scored: inbox placement. No two of these services publish a comparable deliverability number, so a score there would be a guess dressed up as a measurement. Postmark publishes its own time to inbox, and it is the service to read closely if speed to the inbox is the whole job.
What a transactional email API does
A transactional email API sends one message to one person because of something they did: a password reset, a receipt, a one-time code, an order confirmation, a system alert. It is kept apart from marketing email because the two want opposite things. Transactional mail has to arrive in seconds and may reach people who have unsubscribed from marketing. Marketing mail is batched, segmented and sent only to people who agreed to it. Transactional email, defined has the longer version, and transactional email compared with marketing email covers where the line sits.
The API has three jobs. It accepts the message fast and gives you an identifier. It gets the message past the receiving server's checks, which is mostly authentication and reputation. And it tells you what happened, through logs you can search when a customer says the reset never came. The email authentication records are what the second job rests on, and what email deliverability is covers the rest.
The third job is where a support ticket gets answered, and accepted is not delivered. In Nitrosend's delivery events, email.sent means the provider took the message and email.delivered means the recipient's mail server did. Every event carries the idempotency key and tags the message was sent with, so "the reset never came" traces back to one send by your own order or user id. The events are signed in the Standard Webhooks format, so any of its libraries can verify them, and they cover single transactional messages, not campaigns or flows.
Those three jobs are becoming the floor, not the product. George Hartley, Nitrosend's co-founder, said on SaaS Stories in September 2026: "in the future future, there's going to be a bunch of kind of dumb email pipes that these agents will just sit on top of. But we do think we can kind of be smarter than that if we look at actually how can people improve based on all of the volume that's going through." When you compare the services below, the delivery basics should be table stakes; the difference worth paying for is what the provider tells you, or your agent, about what to fix.
The part most teams get wrong
Transactional emails are the most underrated messages in the inbox. They are the emails people open because they asked for them, and most companies treat them as plumbing.
Treating them as plumbing wastes the space. A receipt or a welcome email is a brand moment, because it is the one message you can be sure the customer opens. This is why the tests on this page give 10 points to emails that come out in your brand without a designer. Transactional email best practices has the checklist.
The engineering side is discipline. A receipt with a promotion bolted on can stop being transactional. Under the US CAN-SPAM Act, the FTC judges an email by its primary purpose, and one whose primary purpose is promotion needs an unsubscribe link like any marketing email. Keep the streams apart, keep the receipt a receipt, and test the message you are about to send rather than a copy of it.
Should receipts and newsletters share a domain?
No. Put them on separate subdomains, on day one, before you have a reputation to protect. If notifications.yourapp.com carries password resets and mail.yourapp.com carries campaigns, a campaign that draws complaints cannot drag the resets into spam with it. Providers keep the two apart in different ways: Postmark with message streams on separate IPs, SendGrid with IP pools, Mailgun with dedicated IP pools, and Amazon SES with tenants that separate identities, configuration and reputation. Nitrosend sends a receipt through a single-message call that goes out at once, while campaigns and flows wait as drafts until someone approves them, and its Pro plan covers three customer sending domains, enough for both subdomains. Any of those works, as long as the split is there before the first big send.
Transactional email API FAQ
Nitrosend, with the top score in this review, 83.75 out of 100. It is the only service here an AI assistant can set up and send from with no dashboard and no domain to verify first. A receipt goes out on one call, while newsletters and flows wait as drafts until someone approves them. It writes receipts and resets in your brand with no template to build, and it costs $20 a month for 20,000 emails. Resend is second at 77.5 and Bird third at 76. Pick Postmark if track record comes first, and Amazon SES if unit cost at volume decides it.
Nitrosend. It scores 9 out of 10 on working from your AI assistant, the test worth the most points, because its MCP server, account signup over the API and ready-made sender let an agent in Claude, ChatGPT, Cursor or Codex fire a receipt with nobody opening a dashboard. Resend scores 8 because, by its own AI onboarding docs, a human must create the account and a domain must be verified before the agent can send. Bird scores 8 because, although an agent can create the account, a sending domain has to be verified first. MailerSend scores 8, SMTP2GO and Amazon SES 7 (through AWS's own managed MCP server), Postmark and Mailgun 6, and SendGrid 3, because Twilio's MCP server has two tools that search and retrieve API documentation and none that sends. Best email API for AI agents ranks the field on that job alone.
In Claude, enable the official Nitrosend connector from the Claude directory and sign in. In Claude Code, run claude mcp add --transport http nitrosend https://api.nitrosend.com/mcp and complete the OAuth sign-in. Then ask Claude to send the receipt. It uses the nitro_send_message tool, which sends one transactional email to a single recipient immediately. Give each receipt a stable idempotency key, such as the order number, and a retry of the same request cannot deliver it twice. The Nitrosend MCP docs cover ChatGPT, Cursor and Codex as well.
Accepted in well under a second and delivered within seconds. If password resets routinely take minutes, look at queueing and sender reputation before you blame the provider, and check the email authentication records first. A reset also has a shelf life. OWASP's password reset guidance says reset tokens should be single use and expire after an appropriate period, so a reset delivered hours late is a dead link. When Nitrosend refuses a send for lack of capacity, its docs tell API callers to follow the returned retry time rather than retrying in a loop or treating the refusal as delivered.
A separate path for transactional mail, a dedicated IP once your volume can keep it warm, and logs you can search when a customer says the email never came. Postmark has message streams, and its pricing page lists managed dedicated IPs and 45-day retention. Amazon SES lists managed dedicated IPs, Virtual Deliverability Manager and tenants. Mailgun has dedicated IP pools and IP warm-up, and Bird sells dedicated IPs from Growth. Nitrosend sends receipts through its single-message path, with dedicated IPs as a provisioned paid add-on on Scale or Enterprise. What email deliverability is covers what those controls protect.
Yes. Nitrosend gives 5,000 emails to start, then 500 a month, with full API access. Resend's free plan covers 3,000 a month, capped at 100 a day. Bird and SMTP2GO are free to 1,000 a month. MailerSend is free to 500 a month with a card on file, Postmark to 100 a month, and Mailgun to 100 a day. Amazon SES has no standing free plan, only AWS Free Tier credits for new customers, and SendGrid offers a 60-day trial. The best free email API page ranks the free plans.
Use the HTTP API for anything new. It returns structured errors, avoids connection overhead and is easier to debug. Keep SMTP for legacy systems that cannot speak HTTP. Eight of the nine services here offer an SMTP relay, and Nitrosend is the exception. SMTP vs API email services covers the choice.
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