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 for AI agents that send both receipts and newsletters. It has the top score of the eight reviewed here, 83.75 out of 100. It is the only one of the eight that your AI assistant, whether 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 its MCP server at api.nitrosend.com/mcp, sign in with OAuth, and ask the agent to send. It writes every email in your brand's colors, fonts and voice, and your receipts, newsletters and automated flows go out through one API, 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 Loops at 73.
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 3Loops
73 out of 100Total
- Priced by
- Subscribed contacts, sends unlimited
- Free plan
- 1,000 contacts, 4,000 sends a month
- Entry plan
- $49 a month, up to 5,000 contacts
- Works from your AI assistant8 out of 10Hosted MCP server at mcp.loops.so, a ChatGPT plugin, a CLI and agent skills, but a person signs in and each transactional email is a published template (docs).
- Receipts and newsletters on one plan9 out of 10Campaigns, workflows and transactional email on every plan, through one API or SMTP, with unlimited sends on paid plans (pricing).
- Emails in your brand, no designer5 out of 10Themes set fonts and styles that cascade to every email, set up by hand rather than learned from your site (docs).
- Free plan7 out of 104,000 sends in any rolling 30 days and 1,000 subscribed contacts, with a Loops footer on every email (pricing).
- Price8 out of 10$49 a month on the smallest paid plan at either volume, because Loops prices by subscribed contacts and sends are unlimited (pricing).
- Developer tools7 out of 10Official SDKs for JavaScript, Go, PHP and Ruby, an SMTP service, signed webhooks and a CLI. No inbound email (SDKs).
- Track record and support5 out of 10An SLA and dedicated support come only on the custom Enterprise plan, and no uptime figure is on the pricing page (pricing).
Rank 4Brevo (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 5MailerSend
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 6Customer.io
68 out of 100Total
- Priced by
- Profiles (people and objects)
- Free plan
- None. 14-day trial, 5,000 messages
- Entry plan
- $100 a month, 5,000 profiles, 1M emails
- Works from your AI assistant8 out of 10Hosted MCP server with OAuth, a Claude connector, ChatGPT and Cursor plugins and a CLI that can sign up, but every account is reviewed by a person before it sends (docs).
- Receipts and newsletters on one plan8 out of 10Transactional API, broadcasts and journeys on one Essentials plan with a separate transactional IP pool, though sending and data go through separate APIs (pricing).
- Emails in your brand, no designer8 out of 10Design Studio reads your website to generate styles and a brand document that its AI writing follows (docs).
- Free plan2 out of 10No free plan. A 14-day trial with 5,000 messages, or a year free for startups that raised under $10M (docs).
- Price6 out of 10$100 a month at 5,000 profiles and about $955 at 100,000, with 1,000,000 emails included on Essentials (pricing).
- Developer tools6 out of 10Node, Python and Go data libraries, mobile SDKs, reporting webhooks and test sends, but no SMTP relay into it and no inbound email (docs).
- Track record and support8 out of 10Running since 2012 for 9,000+ brands, with a transactional IP pool, dedicated IPs at $50 each, SOC 2 and HIPAA (docs).
Rank 7Mailjet (Sinch)
62.5 out of 100Total
- Priced by
- Emails sent
- Free plan
- 6,000 emails a month, 200 a day, no expiry
- Entry plan
- Starter, $9 a month, 8,000 emails
- Works from your AI assistant3 out of 10Official MCP server runs on your own computer and registers only read (GET) tools, so an agent cannot send through it (GitHub).
- Receipts and newsletters on one plan8 out of 10Send API, SMTP relay and campaigns share one plan and one email volume, but automations need Premium (pricing).
- Emails in your brand, no designer7 out of 10Brand Kit suggests colors and themes from your website URL and applies them to marketing, transactional and automation templates on paid plans, not voice (help).
- Free plan8 out of 106,000 emails a month, at most 200 a day, up to 1,000 contacts, with the APIs and SMTP relay included and no card (pricing).
- Price6 out of 10$41.90 for 20,000 emails on Premium 15,000 at $29 plus $2.58 per 1,000 after (Premium 50,000 is $59, Essential has no automations), and $1,099 for a million on Premium 500,000 plus overage, or a custom quote (pricing, overage).
- Developer tools8 out of 10Official SDKs in seven languages, SMTP relay, event webhooks, a sandbox mode and the Parse API for inbound, which needs Premium 50k or above (docs).
- Track record and support7 out of 10Sending since 2010, now part of Sinch. A dedicated IP on Premium from 100,000 emails, and an SLA only on custom 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 26, 2026| What we compared | Nitrosend | Resend | Loops | Brevo | MailerSend | Customer.io | Mailjet | SendGrid |
|---|---|---|---|---|---|---|---|---|
| Works from your AI assistant25 points | 9 out of 10 | 8 out of 10 | 8 out of 10 | 5 out of 10 | 8 out of 10 | 8 out of 10 | 3 out of 10 | 3 out of 10 |
| Receipts and newsletters on one plan15 points | 9 out of 10 | 7 out of 10 | 9 out of 10 | 8 out of 10 | 4 out of 10 | 8 out of 10 | 8 out of 10 | 6 out of 10 |
| Emails in your brand, no designer10 points | 9 out of 10 | 6 out of 10 | 5 out of 10 | 7 out of 10 | 6 out of 10 | 8 out of 10 | 7 out of 10 | 5 out of 10 |
| Free plan10 points | 7 out of 10 | 8 out of 10 | 7 out of 10 | 9 out of 10 | 5 out of 10 | 2 out of 10 | 8 out of 10 | 3 out of 10 |
| Price15 points | 8.5 out of 10 | 9 out of 10 | 8 out of 10 | 6 out of 10 | 8 out of 10 | 6 out of 10 | 6 out of 10 | 9 out of 10 |
| Developer tools15 points | 10 out of 10 | 9 out of 10 | 7 out of 10 | 9 out of 10 | 9 out of 10 | 6 out of 10 | 8 out of 10 | 9 out of 10 |
| Track record and support10 points | 4 out of 10 | 6 out of 10 | 5 out of 10 | 7 out of 10 | 6 out of 10 | 8 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 | 73 out of 100,3rd | 70 out of 100,4th | 68.5 out of 100,5th | 68 out of 100,6th | 62.5 out of 100,7th | 59.5 out of 100,8th |
Here are the seven yes-or-no questions teams usually ask before they pick one email API for everything they send. 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, 2026QuestionNitrosendResendLoopsBrevoMailerSendCustomer.ioMailjetSendGrid
NitrosendResendLoopsBrevoMailerSendCustomer.ioMailjetSendGridSend from the chatCan an agent send a transactional email without anyone opening the web app?Nitrosend: Yes.Resend: Yes.Loops: Yes.Brevo: Not a yes or no.MailerSend: Yes.Customer.io: Yes.Mailjet: No.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. |
| Loops | Yes. Yes, a published transactional email, once a person has signed in and connected the MCP server. |
| 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. |
| Customer.io | Yes. Yes, through the hosted MCP server with the live-send scope, after the account passes manual review. |
| Mailjet | No. No. The MCP server exposes only read endpoints, so it cannot send. |
| 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.Loops: Yes.Brevo: Yes.MailerSend: Yes.Customer.io: Yes.Mailjet: 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. |
| Loops | Yes. Yes. mcp.loops.so, with 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. |
| Customer.io | Yes. Yes. mcp.customer.io/mcp, with OAuth and scoped permissions. |
| Mailjet | No. No. The MCP server runs locally through npx with your API key. |
| 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.Loops: No.Brevo: No.MailerSend: No.Customer.io: No.Mailjet: 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. |
| Loops | No. No. A person signs in to Loops in a browser. |
| 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. |
| Customer.io | No. No. The CLI can start a signup, but every account is reviewed by hand before it can send. |
| Mailjet | No. No. A person signs up in the web app and copies the API keys. |
| 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.Loops: Yes.Brevo: Yes.MailerSend: No.Customer.io: Yes.Mailjet: 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. |
| Loops | Yes. Yes. Campaigns, workflows and transactional on every 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. |
| Customer.io | Yes. Yes. Transactional, broadcasts and journeys are all on Essentials. |
| Mailjet | Not a yes or no. Campaigns and the Send API share every plan, but flows start on Premium. |
| 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.Loops: Yes.Brevo: Yes.MailerSend: Yes.Customer.io: No.Mailjet: 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. |
| Loops | Yes. Yes. 4,000 sends in any 30 days, with a Loops footer. |
| Brevo | Yes. Yes. 300 emails a day with no time limit. |
| MailerSend | Yes. Yes. 500 emails a month. |
| Customer.io | No. No. A 14-day trial, or 12 months free for qualifying startups. |
| Mailjet | Yes. Yes. 6,000 emails a month, 200 a day, no time limit. |
| 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.Loops: No.Brevo: Yes.MailerSend: No.Customer.io: Yes.Mailjet: Yes.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. |
| Loops | No. No. Themes are set up by hand. |
| 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. |
| Customer.io | Yes. Yes. Design Studio scrapes your website to generate styles and a brand document. |
| Mailjet | Yes. Yes. Brand Kit suggests colors and themes from a URL, applied on paid plans, not voice. |
| 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.Loops: No.Brevo: Yes.MailerSend: Yes.Customer.io: No.Mailjet: Not a yes or 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. |
| Loops | No. No inbound email in the documentation. |
| Brevo | Yes. Yes. Inbound parsing posts replies to your webhook as JSON. |
| MailerSend | Yes. Yes, through inbound routing. |
| Customer.io | No. No. Inbound handling covers SMS and WhatsApp replies, not email. |
| Mailjet | Not a yes or no. The Parse API handles inbound, but only on Premium 50k and above. |
| 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 7 yes for Loops5 of 6 yes for Brevo4 of 7 yes for MailerSend4 of 7 yes for Customer.io2 of 5 yes for Mailjet1 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, Loops 73, Brevo 70, MailerSend 68.5, Customer.io 68, Mailjet 62.5, 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
This page ranks services on both jobs at once, the receipts and resets your app triggers and the newsletters and flows your marketing sends, from one API. If transactional email is the only job, the ranking of transactional email APIs for AI agents compares the specialists on speed, deliverability controls and price instead. Nitrosend does not win every test here. Read these before you choose it.
- Pick Resend if most of what you send is 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. Its broadcasts and automations sit on a separate marketing plan priced by contacts. The Nitrosend and Resend comparison goes test by test.
- Pick Loops if you want the lowest flat price for receipts and campaigns together. Loops prices by subscribed contacts, and transactional email to people who are not on your list is unlimited on every paid plan, so $49 a month covers 20,000 or a million receipts. It matches Nitrosend on one plan for both jobs, 9 to 9, and it scores 7 on developer tools, with SDKs in four languages and an SMTP service. The price climbs with your subscribed list. See Nitrosend and Loops compared.
- Pick Brevo if you want the largest free plan and a drag-and-drop editor. Its Free plan sends 300 emails a day once Brevo approves the account, which earns it a 9 on free plan against Nitrosend's 7. It also scores 9 on developer tools, with official SDKs in seven languages and inbound parsing. Automated emails start on Standard, $69 for 20,000 emails. See Nitrosend and Brevo compared.
- Pick Customer.io if you already run lifecycle journeys across channels. It scores 8 on track record against Nitrosend's 4, with a separate, stricter IP pool for transactional mail, and its hosted MCP server can send once an admin grants the live-send permission. There is no free plan, every account is reviewed by hand before it can send, and Essentials is $100 a month at 5,000 profiles.
- Pick Mailjet if you want a generous free plan to start campaigns on. It sends 6,000 emails a month free, 200 a day, with the APIs and SMTP relay included, and it scores 8 on free plan. Campaigns and the Send API share every plan, but automated flows start on Premium, and its MCP server is a read-only connection. See Nitrosend and Mailjet compared.
- Pick MailerSend if you want a full developer kit at a middle price. It scores 9 on developer tools, and it is $35 for 20,000 emails on Starter and $600 for a million. It sends bulk email through the same API but has no campaign builder or flows, so it ranks higher on the transactional list. See Nitrosend and MailerSend compared.
- Pick SendGrid if you already run on Twilio. It scores 8 on track record and 9 on developer tools, and Twilio is one vendor for SMS, voice and email. Email API and Marketing Campaigns are billed as two products on two different units, and in place of a free plan it offers a 60-day trial at 100 emails a day. See Nitrosend and SendGrid compared.
What each one costs in 2026
Six of these services charge by emails sent. Loops charges by subscribed contacts, and transactional email to people not on your list is unlimited on every paid plan, so its price is the smallest paid plan at both volumes. Customer.io charges by profiles, so it is priced at 5,000 profiles for the first volume and 100,000 for the second, with 1,000,000 emails included on Essentials. Brevo is priced at Standard, the first plan with automated emails, because Nitrosend's $20 includes automated flows, so Standard is the fair comparison in functionality. Brevo's Starter is $32 at 20,000 emails without them.
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 |
| Loops (pricing page) | $49The 1,001 to 5,000 contacts plan, sends unlimited | $49Lowest. The same plan. Transactional sends are unlimited on every paid plan |
| 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 |
| Customer.io (pricing page) | $100Essentials, 5,000 profiles and 1,000,000 emails included | $955Essentials at 100,000 profiles, $100 plus 95,000 extra profiles at $0.009, 1,000,000 emails included |
| Mailjet (pricing page) | $41.90Premium 15,000 at $29, and $2.58 per 1,000 after. Premium 50,000 is $59, Essential has no automations | $1,099Premium 500,000 at $499, and $1.20 per 1,000 after, or a custom quote |
| SendGrid (pricing page) | $19.95Lowest. Essentials, 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 a nickel more than SendGrid at $19.95. MailerSend is $35, Mailjet $41.90 on Premium, Loops $49, Brevo $69 on Standard and Customer.io $100. Mailjet and Brevo are priced at their first plan with automated emails, the fair comparison with Nitrosend's $20.
At a million emails a month, Nitrosend is $650. MailerSend is $600, Resend $650, SendGrid $799, Customer.io about $955, Brevo $999 and Mailjet $1,099. Only Loops costs less, $49 for transactional email to people not on your list, and it climbs with your subscribed list once you send it campaigns, because it prices the list rather than the sending.
The bigger difference is what the $20 buys. Nitrosend's own API page puts it plainly: most email APIs stop at "send a message", and Nitrosend gives you the entire stack through the same key, lists, automation, segmentation, brand and deliverability, alongside a single-call transactional send. Resend sells marketing as a second plan priced by contacts, and SendGrid sells Marketing Campaigns as a separate product. If you would otherwise buy a second product for campaigns, add the two bills together before you compare. The full email API comparison lays the wider field out in one table.
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: Claude, ChatGPT, Cursor and other assistants now reach outside tools through the Model Context Protocol, an open standard, so the email API an assistant can run end to end is the one it will use. Receipts and newsletters on one plan is worth 15 points, because that is the job this page ranks. 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 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.
These are the same tests, scores and prices as every ranked page on this site, including the 8 best email API services review.
What decides whether you are happy in a year
Four things predict whether a team is still happy with its email API a year after choosing it. None of them is on a pricing page.
How the streams are kept apart. Cold outreach, marketing email and transactional email are different jobs with different domains, volumes and rules. A provider that treats them as one problem creates incidents. A provider that forces them into two vendors creates a seam, two DNS setups and two suppression lists that drift apart. Look for one account that keeps the streams apart inside it. Gmail's sender guidelines ask for a different From address for each type of message, receipts apart from promotions, and a different IP for each type if you send from more than one. Inside one account the sending paths should differ too. In Nitrosend a transactional email is a single call that goes out at once, while a campaign or flow is a draft that never delivers until someone approves it (MCP tools), so a password reset never waits behind a newsletter's review. Transactional email compared with marketing email covers the split.
What moving costs. Moving your sending is not a settings change. Gmail's guidelines tell a sender with no history to start with low volume to engaged people and increase it slowly, so a migration carries weeks of ramp before a big send goes out at full speed. That cost is on no pricing page. Two things shorten it. One is keeping the provider you already send through, covered below. The other is a provider that judges evidence rather than calendar days: Nitrosend's pricing docs say enough delivery history can qualify an account on day one, payment alone does not earn trust, and a trusted account gets its full allowance without a second ramp. How to warm up an email domain has the schedule to plan against.
How it behaves under load. Throughput, queueing and the ramp a new sender is held to decide whether your first big send goes out at all. Best email sending API ranks the field on that job, and email bounce rate is the number to watch while you ramp.
Whether an assistant can run it. This is the newest difference and the one the category has been slowest to meet. Agent traffic is already moving past chat: in Nitrosend's own MCP logs, some packaged clients query an account on a schedule rather than waiting for a person to type. What MCP is explains the protocol, and best email API for AI agents ranks the field on that job alone.
George Hartley, Nitrosend's co-founder, describes the job he built Nitrosend for as the whole stack, not one send. On DESIGNWAVE in August 2026 he said: "whether it's outbound flows, the transactional emails, newsletters, even email inboxes, just to be able to run that whole stack and be the smart pipes behind your agent." Three weeks later on The Breakout CEO he gave the reason: "this agentic kind of explosion is about to happen. I don't know how or what it looks like. And okay, let's, let's build some, let's build the best smart pipes for them to kind of communicate." That is the bet behind scoring an API on what an assistant can run, not only on what it can send.
One warning if you let an assistant pick for you. Language models guess when they are uncertain and state plausible answers that are wrong, and email is full of rules that sound plausible. An assistant will name a deliverability rule with no source as readily as one Gmail publishes. Ask it for the mechanism and the source, not the recommendation.
Can I keep my current sending provider and add campaigns on top?
Yes, and it is usually the lower-risk move. On paid plans Nitrosend supports bring-your-own sending keys for SendGrid, Mailgun, Postmark, Resend and Amazon SES, and its docs describe the route for teams that already have reputation, volume pricing or compliance terms tied to an existing provider account. Point it at the key you already have and you keep the same sending reputation, IPs and warm-up history, while lists, segments, flows and reporting move over. Nothing on the transactional path changes on day one. It is also why a team that only needs the lowest unit cost can run Amazon SES underneath and keep Nitrosend on top. The bring-your-own sending keys page has the mechanics.
Best email API FAQ
Nitrosend, with the top score in this review, 83.75 out of 100. 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 receipts, lists, segments and flows come on the same key, from $20 a month. Pick Resend if most of what you send is transactional email from application code, Loops if you want one flat price, and Brevo if the free plan decides it.
Yes. Nitrosend, Loops, Brevo and Customer.io put transactional email, campaigns and automated flows on one plan. Mailjet shares one plan for receipts and campaigns, but its flows start on Premium. Resend keeps broadcasts and automations on a separate marketing plan, SendGrid sells Marketing Campaigns as a separate product, and MailerSend sends bulk email with no campaign builder or flows. Transactional email compared with marketing email covers why the two streams still need keeping apart inside one account.
An email API is an HTTP interface that accepts a message from your application and takes responsibility for delivering it. It handles authentication, queueing, retries, bounce processing and event reporting for you. The email API guide covers how one works, and transactional email, defined covers the messages most teams send through it first.
Several. Nitrosend gives 5,000 emails to start, then 500 a month, with full API, MCP and CLI access and flows included. Brevo sends 300 emails a day once it approves the account. Mailjet is free to 6,000 emails a month, 200 a day. Loops allows 4,000 sends every 30 days to 1,000 contacts, with a Loops footer. Resend is free to 3,000 emails a month, capped at 100 a day, and MailerSend to 500 a month with a card on file. SendGrid offers a 60-day trial and Customer.io a 14-day trial, with no free plan. The best free email API page ranks the free plans.
Nitrosend. Nitrosend, Resend, Loops, Brevo, Customer.io and MailerSend host an MCP server your assistant can connect to. Mailjet's runs locally and only reads data, and SendGrid has no first-party server that sends. Brevo's server manages campaigns but documents no tool for sending a transactional email, and Customer.io's sends after the account passes manual review. Only Nitrosend lets the agent create the account and get a ready sender without a person verifying a domain first. Best email API for AI agents ranks the field on that job alone.
Connect Nitrosend's MCP server at api.nitrosend.com/mcp and sign in with OAuth. In Claude it is a connector in the Claude directory. In Claude Code it is one command, claude mcp add --transport http nitrosend https://api.nitrosend.com/mcp. ChatGPT connects through its plugin directory, and Cursor through /add-plugin nitrosend. Then ask for the email. A receipt or reset goes out at once, with an idempotency key so a retry cannot send it twice, and a newsletter or flow is saved as a draft until someone approves it. The Claude Code setup guide has the steps.
Nitrosend publishes it, and it ranks first on seven tests that are printed in full above, with every score, reason and source on the cards. The same tests are used on every ranked page on this site, and the points for each test were set before any service was scored. Where another service is the better pick, the section above says so by name.
Go deeper
Compare by use case