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 email sending API for teams that run email from AI, with the top score of the eight reviewed here, 83.75 out of 100. It scores 9 out of 10 on working from your AI assistant, the heaviest test, and it is the only one of the eight that Claude, ChatGPT, Cursor or Codex can sign up to and send from without anyone opening a dashboard. To send email from an AI agent with Nitrosend, connect the agent to its MCP server at api.nitrosend.com/mcp and sign in with OAuth. A single transactional email then goes out in one call, and a campaign or flow stays a draft until it is approved. Every send takes an Idempotency-Key, so a retry after a timeout cannot become a second email, and your receipts and newsletters go out from one account on one plan. It costs $20 a month for 20,000 emails and $650 for a million emails on Scale including overage. Resend comes next at 77.5, then Brevo at 70.
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 3Brevo (formerly Sendinblue)
70 out of 100Total
- Priced by
- Emails sent
- Free plan
- 300 emails a day, no expiry
- Entry plan
- Starter, $9 a month, 5,000 emails
- Works from your AI assistant5 out of 10Hosted MCP server at mcp.brevo.com with a token a person creates, but its modules list no tool that sends a transactional email (docs).
- Receipts and newsletters on one plan8 out of 10Transactional email by API and SMTP on every plan, counted in the same monthly volume as campaigns, with automation from Standard (pricing).
- Emails in your brand, no designer7 out of 10The brand library fetches a logo, colors, fonts and social links from your website into the email editor, but not a tone of voice (help).
- Free plan9 out of 10300 emails a day, about 9,000 a month, with transactional email and up to 100,000 contacts, free forever (help).
- Price6 out of 10$69 a month for 20,000 emails on Standard, the first plan with automated emails (Starter is $32 without them), and $999 for a million on Professional (pricing).
- Developer tools9 out of 10Official SDKs in seven languages, an SMTP relay, transactional webhooks, a sandbox header and inbound email parsing (docs).
- Track record and support7 out of 10Sending since 2012 as Sendinblue. Dedicated IPs are an add-on from Professional, and an SLA comes only with Enterprise (help).
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 8SendGrid
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 | Brevo | MailerSend | Mailgun | SES | Postmark | SendGrid |
|---|---|---|---|---|---|---|---|---|
| Works from your AI assistant25 points | 9 out of 10 | 8 out of 10 | 5 out of 10 | 8 out of 10 | 6 out of 10 | 7 out of 10 | 6 out of 10 | 3 out of 10 |
| Receipts and newsletters on one plan15 points | 9 out of 10 | 7 out of 10 | 8 out of 10 | 4 out of 10 | 4 out of 10 | 3 out of 10 | 4 out of 10 | 6 out of 10 |
| Emails in your brand, no designer10 points | 9 out of 10 | 6 out of 10 | 7 out of 10 | 6 out of 10 | 5 out of 10 | 2 out of 10 | 5 out of 10 | 5 out of 10 |
| Free plan10 points | 7 out of 10 | 8 out of 10 | 9 out of 10 | 5 out of 10 | 7 out of 10 | 4 out of 10 | 4 out of 10 | 3 out of 10 |
| Price15 points | 8.5 out of 10 | 9 out of 10 | 6 out of 10 | 8 out of 10 | 8 out of 10 | 10 out of 10 | 8 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 | 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 | 8 out of 10 |
| Total scoreout of 100 | 83.75 out of 100,1st | 77.5 out of 100,2nd | 70 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 | 59.5 out of 100,8th |
Here are the seven yes-or-no questions developers usually ask before they pick a sending API. 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.
8 services, side by side
Checked September 26, 2026QuestionNitrosendResendBrevoMailerSendMailgunSESPostmarkSendGrid
NitrosendResendBrevoMailerSendMailgunSESPostmarkSendGridSend from the chatCan an agent send a transactional email without anyone opening the web app?Nitrosend: Yes.Resend: Yes.Brevo: Not a yes or no.MailerSend: Yes.Mailgun: Yes.SES: Not a yes or no.Postmark: 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. |
| Brevo | Not a yes or no. The hosted MCP server creates and manages campaigns, but no tool for sending a transactional email is documented. |
| 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. |
| 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.Brevo: Yes.MailerSend: Yes.Mailgun: No.SES: No.Postmark: No.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. |
| Brevo | Yes. Yes. mcp.brevo.com, signed in with a token a person generates in the web app. |
| 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. |
| 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.Brevo: No.MailerSend: No.Mailgun: No.SES: No.Postmark: 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. |
| Brevo | No. No. A person creates the account and the MCP token, and Brevo approves the account before it sends. |
| 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. |
| 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.Brevo: Yes.MailerSend: No.Mailgun: No.SES: No.Postmark: Not a yes or 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. |
| Brevo | Yes. Yes. Transactional is on every plan and automation runs from Free up to 2,000 contacts and from Standard without a limit. |
| 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. |
| 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.Brevo: Yes.MailerSend: Yes.Mailgun: Yes.SES: No.Postmark: 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. |
| Brevo | Yes. Yes. 300 emails a day with 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. |
| 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.Brevo: Yes.MailerSend: No.Mailgun: No.SES: No.Postmark: 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. |
| Brevo | Yes. Yes. The brand library fetches logo, colors, fonts and links from a URL, not tone of voice. |
| 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. |
| 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.Brevo: Yes.MailerSend: Yes.Mailgun: Yes.SES: Yes.Postmark: Yes.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. |
| Brevo | Yes. Yes. Inbound parsing posts replies to your webhook as JSON. |
| 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. |
| 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 Resend5 of 6 yes for Brevo4 of 7 yes for MailerSend3 of 7 yes for Mailgun1 of 6 yes for SES3 of 6 yes for Postmark1 of 6 yes for SendGrid
At a glance
8 services, the same 7 tests, 100 points in all. In order: Nitrosend 83.75, Resend 77.5, Brevo 70, MailerSend 68.5, Mailgun 67.5, SES 65.5, Postmark 64.5, 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
Nitrosend does not win every test. Read these before you choose it.
- Pick Amazon SES if raw throughput at the lowest cost is the job. It is $3.20 for 20,000 emails and $160 for a million on Essentials, which earns it a 10 on price, and it scores a 9 on developer tools and on track record. The catch is that SES is infrastructure. Templates, suppression handling and reporting are yours to build, and a new account starts in the SES sandbox until a person requests production access.
- Pick Postmark or Mailgun if you want the longest record of sending at scale. Both score a 9 on track record and support, and both sell dedicated IPs. Postmark keeps transactional and broadcast mail in separate message streams, and Mailgun lists a guaranteed uptime SLA and inbound routing.
- Pick Resend if you want the fullest kit in code. It scores 9 on developer tools, with official SDKs, an SMTP relay, inbound email and React Email on every plan.
- Pick Brevo if you want the biggest free allowance and SMTP. It scores a 9 on free plan, with 300 emails a day, and a 9 on developer tools, with official SDKs in seven languages, an SMTP relay and inbound parsing. It is $32 for 20,000 emails, but $999 for a million.
- Pick MailerSend if you want a full 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.
- Pick SendGrid if you already run on Twilio. Its free plan is now a 60-day trial at 100 emails a day, so budget for Essentials at $19.95 from the first month.
What each one costs in 2026
Every service here charges by emails sent except Amazon SES, which 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 since 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 |
| Brevo (pricing page) | $69Standard, the first plan with automation. Starter is $32 without it | $999Professional. Standard stops at 500,000 emails |
| 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 |
| 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 and a nickel more than SendGrid at $19.95. Postmark is $29.50, Mailgun $33, MailerSend $35 and Brevo $69 on Standard, the plan priced here because it is the first with automated emails, the fair comparison with Nitrosend's $20 (Starter is $32 without them).
At a million emails a month, Nitrosend is $650. MailerSend is $600, Resend $650, Mailgun $700, Postmark $775, SendGrid $799 and Brevo $999. With Amazon SES the templates, unsubscribe handling and reporting are yours to build.
A million a month is also where the ramp matters more than the price. Whichever service you pick, the first month at that volume is held back by the ramp described below, so plan the move before the bill forces it. Nitrosend's $650 also carries campaigns and flows on the same key, so if you would otherwise pay for a second product, 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. Coding assistants now add a hosted tool server with one command and a browser sign-in, as OpenAI's Codex guide to MCP shows, so the first thing a new sending API meets is often an assistant asked to wire it up. The test is whether that assistant can get from sign-up to a delivered email without handing the job back to a person. Price, developer tools and track record, where the specialist sending 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?
Two things are not scored. Inbox placement, because no two of these services publish a comparable deliverability number. And raw throughput, because none of them publishes a comparable ceiling for a new account, and every one of them holds a new sender to a ramp.
What a sending API does after it says yes
An email sending API is the part of a provider that takes your message and gets the receiving mail server to accept it: queueing, throughput, retries, bounce and complaint handling, and the limits that decide how fast you may go. A 200 response means the provider has taken the message. Everything that decides whether it reaches an inbox happens after that.
- Queueing and retries. A receiving server that answers "try later" is normal, and the provider holds the message and tries again. The mail standard, RFC 5321, says a sender should keep retrying for at least 4-5 days before it gives up. That suits a newsletter. It does not suit a password reset, which OWASP's reset guidance says should expire after a set period, so a reset that lands two days late is a dead link. Ask each provider how long it retries a transactional message.
- Failures. A send that has failed for good should reach your code, or your agent, as an event it can act on, such as fixing the address and sending again. Nitrosend's
email.failedwebhook fires only once a send has failed for good, never while it is still being retried, so nothing gets resent while the first copy may still arrive. - Bounces. A hard bounce should put the address on a suppression list at once, and for the whole account, not one campaign. Every service on this page does this automatically. Email bounce rate covers the thresholds that matter.
- Complaints. When a recipient marks a message as spam, the mailbox provider reports it back, and the address should be suppressed just as fast.
- Events. Delivery, bounce and complaint events come back to your application, and email webhooks cover how that works. Opens and clicks need a filter. Company mail security such as Microsoft Defender's Safe Links checks the links in a message before it is delivered, so a raw click count can include the scanner as well as people. Nitrosend reports only the first human click on each link and leaves security scanners and bots out of its open events.
- Duplicates. A retry after a timeout, whether your code or an agent makes it, must not become a second email. Nitrosend accepts an
Idempotency-Keyheader on a send for exactly this, and a retry with the same key does not send again. It is the same pattern Stripe documents for retrying a payment safely.
Why a new sender is held back
Every provider limits how fast a new sender can go, and it is the most common frustration in this category. It is also correct. Mailbox providers judge you on your sending pattern, and Google's sender guidelines warn that suddenly doubling your volume can get you rate limited or cost you reputation.
Warm up gradually and raise volume with each send, especially with a large list. If you are moving providers, do not assume your old reputation comes with you, because reputation belongs to the sending domain and IP, not to you. How to warm up an email domain covers the ramp, and IP warming covers dedicated IPs. Google Postmaster Tools is the free source of truth for Gmail while you do it.
Nitrosend meters sending capacity separately from email credits. On the Free plan it is 100 recipients per rolling 24 hours, rising as the account builds a delivery record, so a large first import is held to the same ramp as everywhere else.
One kind of mail should not go through a bulk sending API at all. George Hartley, Nitrosend's co-founder, put it plainly on SaaS Stories in September 2026: "outbound actually sort of has to run from email addresses, right? You can't run outbound through a bulk system because that's immediately going to cook everything like Gmail will just cut you off." His answer for agents that do outreach is a mailbox of their own: "agents need their own email addresses." He described the same turn on The Breakout CEO in August, once agents could sign up and send on their own: "Oh, actually they need an inbox as well." So keep one-to-one outreach on individual mailboxes, and use a sending API for the receipts, notifications and campaigns your recipients asked for.
Email sending 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 sign up to and send from without anyone opening a dashboard, while a campaign or flow still waits as a draft until it is approved. Sends take an idempotency key so retries cannot double up, and campaigns and flows run on the same plan from $20 a month. Pick Amazon SES for raw throughput at the lowest cost, and Postmark or Mailgun for the longest record of sending at scale.
Because your sending domain and IP have not built a reputation yet. Limits rise as you send steadily to people who engage. It is a reputation system, not a billing tactic, and every service on this page has one.
A hard bounce should put the address on a suppression list at once, for the whole account. A soft bounce is retried for a window before it is treated as a failure. Every service here does this automatically. Email bounce rate covers the thresholds.
The API, for anything new. It returns structured errors, tells you at once whether the message was accepted and gives you an identifier to track it. Keep SMTP for legacy systems that speak nothing else. Seven of the eight services here offer an SMTP relay, and Nitrosend sends through its API, CLI and MCP server only. SMTP vs API email services covers the choice.
Validate the list first, then ramp up gradually from a warmed domain. Importing a large unvalidated list and sending to all of it is the fastest way to hit a bounce threshold and stall. Best email validation API ranks the services that clean a list first.
Nitrosend, which scores 9 out of 10 on working from your AI assistant, ahead of Resend and MailerSend at 8. Nitrosend, Resend, MailerSend and Brevo host MCP servers an assistant can connect to, and Postmark and Mailgun publish ones you run yourself. Of the eight here, only Nitrosend lets the agent create the account and get a ready sender without a person verifying a domain first. Best email API ranks the wider field.
In Claude Code, run claude mcp add --transport http nitrosend https://api.nitrosend.com/mcp and finish the sign-in. In Codex, run codex mcp add nitrosend --url https://api.nitrosend.com/mcp, then codex mcp login nitrosend. Claude.ai, Claude Desktop and ChatGPT connect through their own connector and app directories, with no key to paste. Then ask for the email. A single transactional email goes out at once with an idempotency key, and a campaign or flow is saved as a draft until it is approved. Connecting Claude Code covers the first setup.
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