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 API service for teams that run email from an AI agent, with the top score of 83.75 out of 100 across the eight reviewed here. It is the only one of the eight here your AI assistant, whether Claude, ChatGPT, Cursor or Codex, can sign up to and send from without anyone opening a dashboard. To set it up, add Nitrosend's MCP server, https://api.nitrosend.com/mcp, to Claude, Cursor or Codex and sign in with OAuth, or install the Nitrosend app in ChatGPT. Campaigns and flows then stay drafts until approved, and a single transactional email sends on the call. It writes every email in your brand's colors, fonts and voice, and your receipts and newsletters go out on one plan and one bill. 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 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 4Mailgun
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 5Amazon 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 6Postmark
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 7SMTP2GO
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 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 25, 2026| What we compared | Nitrosend | Resend | Bird | Mailgun | SES | Postmark | SMTP2GO | SendGrid |
|---|---|---|---|---|---|---|---|---|
| Works from your AI assistant25 points | 9 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 | 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 | 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 | 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 | 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 | 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 | 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 | 67.5 out of 100,4th | 65.5 out of 100,5th | 64.5 out of 100,6th | 60 out of 100,7th | 59.5 out of 100,8th |
Here are the seven yes-or-no questions developers usually ask before they pick one of these services. 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 25, 2026QuestionNitrosendResendBirdMailgunSESPostmarkSMTP2GOSendGrid
NitrosendResendBirdMailgunSESPostmarkSMTP2GOSendGridSend from the chatCan an agent send a transactional email without anyone opening the web app?Nitrosend: Yes.Resend: Yes.Bird: 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. |
| 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.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. |
| 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.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. |
| 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.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. |
| 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.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. |
| 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.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. |
| 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: Yes.Resend: Yes.Bird: Yes.Mailgun: Yes.SES: Yes.Postmark: Yes.SMTP2GO: No.SendGrid: Yes.
| Service | Answer |
|---|---|
| Nitrosend | Yes. Yes. An agent inbox on your own domain posts incoming mail to your webhook. |
| Resend | Yes. Yes, on every plan. |
| Bird | Yes. Yes. Inbound domains and relay webhooks. |
| 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 service7 of 7 yes for Nitrosend4 of 5 yes for Resend4 of 5 yes for Bird3 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
8 services, the same 7 tests, 100 points in all. In order: Nitrosend 83.75, Resend 77.5, Bird 76, 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 25, 2026.
When another service is the better pick
Nitrosend does not win every test. Read these before you choose it.
- Pick Resend if you only send transactional email from application code. It scores 9 on developer tools, with official SDKs across languages, an SMTP relay, inbound email and React Email on every plan. It also scores higher on free plan and on track record.
- Pick Bird if the first $5 a month matters. It is $15 a month for 20,000 emails, against Nitrosend's $20, though $530 for a million against Nitrosend's $650. It matches Resend on developer tools, and it hosts its own MCP server at mcp.bird.com with OAuth sign-in.
- 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 Essentials, which earns it a 10 on price. The catch is that SES is infrastructure rather than a product. The templates, suppression handling and reporting are yours to build, and a person opens the AWS account, verifies a domain and requests production access before anything sends.
- Pick Postmark, Mailgun or Amazon SES if track record comes first. Each scores a 9 on track record and support, for years of transactional sending at scale, dedicated IPs, separate streams and published uptime commitments. Postmark refuses bulk mail on its transactional streams, and that refusal is why its delivery times are what they are.
- Pick SendGrid if you need the most room to grow. It still has the widest scale headroom in the category. Its free tier ended on July 26, 2025, replaced by a 60-day trial at 100 emails a day, and Email API and Marketing Campaigns are billed as two products on two different units.
What each one costs in 2026
Every service here charges by emails sent, except two. 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 since July 21, 2026. SendGrid bills its Email API on a send-volume slider and Marketing Campaigns on stored contacts, so if you want both, you pay twice, on two different units.
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) | $20Starter, 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 |
| 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, where most teams start, Nitrosend is $20. That is the same as Resend, and within a few dollars of Bird at $15 and SendGrid at $19.95. Postmark, Mailgun and SMTP2GO charge for every email past 10,000, which puts them at $27 to $33.
At a million emails a month, Nitrosend is $650. SMTP2GO is $520, Bird $530, Resend $650, Mailgun $700, Postmark $775 and SendGrid $799. With Amazon SES the templates, unsubscribe handling and reporting are yours to build. Once your list is large, what email marketing really costs has the wider math.
The bigger difference is what the $20 buys. Nitrosend's own developer page puts it plainly: most email APIs stop at "send a message", and Nitrosend provides the entire stack through the same key, lists, segments, automated flows, brands, templates and deliverability, alongside a single-call transactional send. If you would otherwise buy a second product for campaigns, 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 older 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 25, 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.
Working from your AI assistant carries 25 points because that is where sending is moving. The Model Context Protocol is now the common way to plug a tool into an assistant, supported by Claude, ChatGPT, Cursor and Visual Studio Code among others, according to the protocol's own documentation. Having an MCP server is not the same as an agent being able to send through it. Twilio's MCP server is read-only: it searches API documentation and does not execute API calls. So the test asks whether an agent can do the whole job, from an empty account to a delivered email and a report on what happened. The older services were built around a dashboard and a large feature set, and rebuilding all of that to run from a chat window is a large job, which is why most of them score lower here. Their uptime is not in question.
Receipts and newsletters on one plan is worth 15 points for a less obvious reason: the two follow different rules. Gmail requires one-click unsubscribe on marketing and promotional mail and excludes transactional messages such as password resets, according to Google's sender guidelines FAQ. Postmark keeps transactional and broadcast traffic on separate streams and IP ranges, which it says follows inbox providers' advice on separating reputation (Postmark's Message Streams page). One account therefore has to keep the two apart underneath while letting one assistant see both. When receipts and campaigns run on two providers, whoever owns each one rarely sees the other's email. On one account, the assistant can report on everything going out.
What you get from an email API
Three things: delivery, developer tools, and a way for your AI assistant to run both. Vendors differ far more on the last two.
Outbound delivery. Transactional streams carry one-to-one messages set off by something a user did: receipts, password resets, invitations, new accounts. Marketing streams carry one-to-many sends. Providers keep the two apart to protect reputation. A newsletter at Gmail's 0.3% spam-rate limit, set in Google's email sender guidelines, should not be able to drag a password reset into the spam folder, and a provider that pools both on one reputation lets it. Transactional email compared with marketing email covers the split.
Developer tools. This is where most of the choice gets made. Nitrosend scores 10 here: a REST API with an OpenAPI spec, a typed TypeScript SDK, a CLI, an MCP server, signed event webhooks, idempotent sends and test sends.
- Webhooks. Real-time HTTP events sent back to your application on delivery, open, click, bounce and complaint. Providers differ on retries, signing and how long they keep events. How webhooks work covers the pattern, and securing webhooks covers the signature.
- Inbound email parsing. Incoming replies turned into JSON your application can read. Postmark, Mailgun, SendGrid, Resend, Bird and Amazon SES all offer it over a webhook. Nitrosend's Agent Inbox does too, one address at a time, and exposes each thread over REST and
MCP. - List hygiene and validation. Checking syntax and mailbox status before you send. Mailgun sells this as a product in its own right, and most others expect you to bring a verification service. With a separate verification service, cleaning a list before a campaign means an export and an import back. Nitrosend runs validation as a prepaid API operation, and an import never starts a paid check automatically, so nobody is billed for validating a list they only meant to store.
- Suppression and multiple sending domains. Easy to ignore until you run several products on one account. Enterprise teams in particular value a separate custom sending domain per brand, so a marketing domain and a product domain never share reputation. In Nitrosend, one account can send for several brands, and each sender keeps its own reputation and capacity, so one brand cannot borrow another's trust (Nitrosend's notes on sending at scale).
Working from your AI assistant. The newest part, and the one this review gives the most points. An agent needs an MCP server whose tools cover the whole job, a sender it can use before anyone edits DNS, a test send, an approval step and a way to read back what happened. Nitrosend covers each one: its MCP tools draft, test, approve and send, a shared sandbox sender lets the first test go out before a domain is verified, Brand Kit keeps every draft in your colors, fonts and voice, and the agent reads the analytics back through the same server.
George Hartley, Nitrosend's co-founder, gives that last part the most weight because of what he sees in Nitrosend's own usage. On SaaS Stories in September 2026 he said: "94% of our usage is via the MCP from an agent doing stuff." He had already said where it leads on X in July: "Soon there'll be 100 billion AI agents. Every one of them needs email."
One risk is specific to agents. An assistant whose tool call times out may simply try again, and a repeated POST can send the same receipt twice. The IETF draft for the Idempotency-Key header exists to make POST requests like this fault-tolerant. Nitrosend accepts that header on sends: a retry with the same key and the same message returns the original message rather than sending a second one, and the same key with a different message is refused. Check that any service you let an agent send through does the same.
Email API or SMTP relay: which to use
Both reach the same infrastructure. What differs is the protocol in front of it.
An email API speaks HTTP. It is faster, copes better with bursts and makes attachments simpler. The response tells you at once whether the message was accepted and gives you an identifier to track it, and errors come back structured. If you are writing the code today, use the API.
An SMTP relay speaks the mail protocol. It is slower, chattier and tells you far less, but it is universal. A legacy application, a printer, a CRM or a WordPress plugin will speak SMTP and nothing else, and rewriting them is not worth it. Seven of the eight services here offer both. Nitrosend is the exception. It sends through the API, the CLI and the MCP server, because it was designed for an agent or an application to call, not for a printer. The SMTP relay page has the setup for the others, and webhook versus API covers the event side.
Can I keep my current sending provider and add campaigns on top?
Yes, and it is usually the lower-risk move. Nitrosend supports bring-your-own sending keys for SendGrid, Mailgun, Postmark, Resend and Amazon SES. Point it at the key you already have. You keep the same sending reputation, the same IPs and the same warm-up history, while your contact lists, segments, flows and reporting move over. Nothing on the transactional path changes on day one. That is deliberate, because changing the sending provider and the campaign tools in the same week is how migrations go wrong. The bring-your-own sending keys page has the mechanics, and it is why this review can be specific about where those five beat Nitrosend.
How to switch email APIs without hurting deliverability
Swapping the API takes an afternoon. The reputation takes weeks.
- Add the new DKIM record first. Put the new provider's DKIM record on your sending domain, and list both providers in one SPF record while you overlap. The email authentication page has the records.
- Run both side by side. Split traffic by percentage behind a feature flag, rather than cutting over at once.
- Move the lowest-risk email first. Receipts and password resets go to engaged recipients who expect them, so they warm a new path safely.
- Ramp up over two to four weeks. Raise the percentage in steps and watch bounce and complaint rates at each one. How to warm up an email domain has the schedule.
- Port webhook handling before you send. That way you see delivery events from the new provider while the old one still carries traffic.
- Keep the old provider for a full billing cycle. Check whether a suspended account still bills. Twilio's own SendGrid account review documentation says a suspended account continues to incur auto-renewal billing.
Email API services FAQ
An email API service is infrastructure your application calls over HTTP to send email, so you do not run your own mail server. You POST a message with a recipient, a subject and a body. The service handles queuing, authentication, retries and reputation, then sends delivery, bounce, open, click and complaint events back to you over webhooks. It sits behind password resets, receipts, notifications and, on some providers, marketing campaigns too.
Nitrosend, with the top score in this review, 83.75 out of 100, and the heaviest test here is how well a service works from your AI assistant. It is the only service here where an AI assistant can create the account, get a ready sender and make the first send without a person verifying a domain, and lists, segments and flows come on the same key, from $20 a month. Pick Resend if you are wiring transactional email into application code and want SDKs in many languages and an SMTP relay. Amazon SES suits a team already in AWS that is happy to build the missing pieces.
Several, at different sizes. Nitrosend gives 5,000 emails to start, then 500 a month, with full API, MCP and CLI access on every plan. Resend is free to 3,000 emails a month, capped at 100 a day. Mailgun is free to 100 emails a day. Bird and SMTP2GO are both free to 1,000 emails a month. Postmark's Developer plan is 100 emails a month with no expiry. SendGrid's free tier ended on July 26, 2025, replaced by 60 days at 100 emails a day, and Amazon SES offers new customers up to $200 in AWS credits rather than a free plan.
Postmark, Mailgun, SendGrid, Resend, Bird and Amazon SES all accept inbound mail and hand it to your application as structured data over a webhook. Nitrosend's Agent Inbox does the same for the addresses you set up as inboxes, and exposes each thread over REST and MCP so your code or an agent can read and reply. Mail it quarantines as spam, a virus or a blocked sender is not posted. If your application receives mail at addresses you cannot set up in advance, use one of the others for that part.
Yes, and it is now a normal reason to choose one provider over another. Nitrosend, Resend, Bird, SMTP2GO, Postmark and Mailgun all publish first-party MCP servers, and AWS runs a managed one that can send through Amazon SES, though only Nitrosend, Resend, Bird, SMTP2GO and AWS host theirs, and only Nitrosend, of the eight here, lets the agent create the account and get a ready sender without a person verifying a domain first. Nitrosend's server exposes tools for sending, contacts, segments, flows and reporting, with an approval step before a campaign or flow goes out. Email MCP explains what the protocol does.
Connect Nitrosend once, then ask. In Claude Code, run claude mcp add --transport http nitrosend https://api.nitrosend.com/mcp, then /mcp to sign in with OAuth. In Claude Desktop or Claude.ai, turn on the official Nitrosend connector under Settings, Connectors. Then ask Claude for the email. Brand Kit reads your site for logo, colors, fonts and voice, Claude drafts the message and offers a test send, and a campaign or flow stays a draft until approved. A single receipt or password reset uses the immediate send tool instead. The same server works in Cursor and Codex, and ChatGPT connects through the Nitrosend app.
Bird, formerly MessageBird, acquired SparkPost in 2021 and has retired the name. sparkpost.com now redirects to bird.com, where the email product is sold as Bird Email on the same infrastructure, with the SparkPost developer documentation still served at developers.sparkpost.com. This page scores it as Bird.