I am George Hartley, co-founder of Nitrosend. I have been building email platforms for fifteen years. My last company, SmartrMail, had 12,000 customers and sent more than 6 billion emails before it was acquired in 2022. This list includes our own product, and I will be specific about where it loses.
How this list is ranked
Every comparison of email APIs eventually becomes a comparison of pricing pages. That is the wrong axis, because pricing changes quarterly and the thing that actually hurts you at 2am does not.
So the weights below come from what engineers say they are comparing when they search for this, not from what vendors put on their homepages:
- Deliverability, 20%. Inbox placement, separation of transactional and marketing streams, bounce and complaint handling.
- Developer experience, 20%. Documentation that matches the API, maintained SDKs, time to a first successful send.
- Transactional and marketing on one surface, 15%. Whether password resets and newsletters can live in one system without two vendors and two DNS setups.
- Pricing and free tier, 15%. What it costs to start, and what it costs at 100,000 sends a month.
- Webhooks and analytics, 10%. Signed, retried delivery events, and searchable logs when a customer says they never got the email.
- Agent and MCP surface, 10%. Whether an AI agent can operate the account, not just fire a send.
- Scale and throughput, 10%. Behaviour when volume spikes.
Pricing and capability were checked on 3 September 2026. Treat every dollar figure as a starting point and confirm it on the vendor's own page before you commit.
Best email API 2026, weighted
Checked 3 September 2026| Provider | Transactional + marketing | Native MCP | Free tier | From | Score |
|---|---|---|---|---|---|
| Nitrosend Agent-native | Yes | Yes | 8,000 then 500/mo | $20/mo for 20K | 8.6 |
| Resend | No | Yes | 3,000/mo | $20/mo for 50K | 8.4 |
| Postmark | No | No | Trial only | $15/mo for 10K | 8.0 |
| Amazon SES | No | No | Tiered | $0.10 per 1,000 a la carte | 7.6 |
| MailerSend | No | No | 3,000/mo | $24/mo | 7.2 |
| Loops | Yes | No | 1,000 contacts | $49/mo | 7.0 |
| SendGrid | Separate products | No | 100/day | $19.95/mo for 50K | 6.9 |
| Mailgun | No | No | Trial only | $15/mo for 10K | 6.8 |
1. Nitrosend
Best for: teams that need transactional sending now and marketing sending later, and teams that want an agent to operate the whole account rather than a person operating a dashboard.
Nitrosend is an AI-native email platform driven MCP-first. The same account sends receipts through POST /v1/my/messages, runs campaigns and automation flows, and exposes 28 nitro_* tools so Claude, Codex, Cursor or ChatGPT can operate it directly. There is no dashboard requirement, and there is a human approval gate on sends.
The reason it tops this particular list is the third criterion. Transactional and marketing email are usually two vendors, two DNS configurations and two bills, and the seam between them is where deliverability incidents happen. Nitrosend splits the streams internally so a newsletter cannot crowd out a password reset, but keeps them in one account.
Where it loses: at genuine enterprise volume it is not the cheapest option. Nick, who handles our deliverability and enterprise questions, put it plainly when he was pricing an enterprise lead: at Enterprise size, we would still be more expensive than Klaviyo. And on the marketing side I have said the same thing internally, that we sit cheaper than most email marketing platforms and a bit more expensive than most transactional platforms. If you only ever send transactional mail and you want the floor price, that is Amazon SES and it is not close.
Free tier: 8,000 emails, then 500 a month, with full MCP, API and CLI access on every plan including free. Paid: from $20 a month for 20,000. Contacts are unlimited on every tier, which matters more than it sounds if you are storing a large list and sending to a fraction of it. Email validation is prepaid on all plans rather than included.
Read more on the email API hub or the transactional email API page.
- Nitrosend at a glance
- Verified on the vendor's own pages
- Best for
- teams that need transactional sending now and marketing sending later, and teams that want an agent to operate the whole account rather than a person operating a dashboard
- Pricing model
- per send
- Free tier
- 8,000 emails to start, then 500 a month
- Entry paid plan
- $20/mo (20,000 emails a month, 5 brands, 3 domains, up to 1,000 / 10,000 / 100,000 recipients per rolling 24 hours for Pro Probation / Standard / Trusted)
- At 100,000 emails a month
- $100/mo (Ultra)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- yes
- First-party MCP server
- yes
- Inbound email parsing
- no
- Support
- Help center: docs.nitrosend.com
- Developer docs
- API documentation: docs.nitrosend.com
- Pricing page
- Current pricing
- Limitations
- Not the cheapest at high transactional volume, where Amazon SES wins
- No inbound email parsing over REST, the Agent Inbox is MCP-only
- No cold outreach
- Facts checked
2. Resend
Best for: modern web apps where transactional is the main job, especially React and Next.js codebases.
Resend has the cleanest API and the best documentation in this category, and React Email is a genuinely better way to build templates than raw HTML tables. It also ships an MCP server, resend-mcp on npm, which lets Claude Desktop and Cursor send through it. That MCP is send-focused rather than a full account surface, which is the difference between an agent that can email and an agent that can run your email.
Broadcasts and Automations exist but sit at the simpler end of marketing. If your newsletter needs segmentation and branching flows you will outgrow it.
Free tier: 3,000 a month. Paid: from $20 a month for 50,000. See the Nitrosend and Resend comparison.
- Resend at a glance
- Verified on the vendor's own pages
- Best for
- modern web apps where transactional is the main job, especially React and Next.js codebases
- Pricing model
- per send
- Free tier
- 3,000 emails a month, 100 a day
- Entry paid plan
- $20/mo (50,000 emails a month, extra emails $0.90 per 1,000, 100 AI credits)
- At 100,000 emails a month
- $90/mo (Scale)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- no
- First-party MCP server
- yes
- Inbound email parsing
- yes
- Support
- Help center: resend.com/help
- Developer docs
- API documentation: resend.com/docs
- Status page
- System status: resend-status.com
- Pricing page
- Current pricing: resend.com/pricing
- Limitations
- Broadcasts and Automations sit at the simpler end of marketing
- The MCP server is send-focused rather than a full account surface
- A newsletter needing segmentation and branching flows will outgrow it
- Facts checked
3. Postmark
Best for: high-stakes transactional email where inbox placement beats every other consideration.
If the only thing you send is password resets, receipts and security alerts, Postmark is the safest answer on this list and it wins the deliverability criterion outright. Message Streams are the correct model for stream separation, support is excellent, and the product does not try to be a marketing tool.
That focus is also the limitation. There is no marketing layer and no MCP server, so it scores low on two of the seven weights. Nothing is wrong with the product. It is answering a narrower question.
Paid: from $15 a month for 10,000. See Nitrosend and Postmark compared.
- Postmark at a glance
- Verified on the vendor's own pages
- Best for
- high-stakes transactional email where inbox placement beats every other consideration
- Pricing model
- per send
- Free tier
- Developer trial only
- Entry paid plan
- $15/mo (10,000 emails a month)
- Transactional API
- yes
- Marketing campaigns
- no
- Automation flows
- no
- SMS
- no
- Inbound email parsing
- yes
- Owner
- ActiveCampaign
- Support
- Help center: postmarkapp.com/support
- Developer docs
- API documentation: postmarkapp.com/developer
- Status page
- System status: status.postmarkapp.com
- Pricing page
- Current pricing: postmarkapp.com/pricing
- Limitations
- No marketing layer
- No MCP server, so it scores low on the agent criterion
- Trial only, with no perpetual free tier
- Facts checked
4. Amazon SES
Best for: high volume where you can absorb the operational work.
At $0.10 per 1,000 emails on a la carte pricing, nothing else is close on unit cost, and if you are already inside AWS the IAM and CloudWatch integration is free leverage. Read that figure carefully: SES also sells three plans, and new accounts have defaulted to the Essentials plan at $0.16 per 1,000 since 21 July 2026, so the price you actually pay depends on which structure your account is on. What you are buying is raw sending infrastructure rather than a product: no templates worth using, no campaign layer, no meaningful analytics, and reputation management is your problem.
The sensible pattern for most teams is not to choose between SES and a platform. Nitrosend supports bring-your-own sending keys, so you can run SES underneath and keep the platform on top. We are one of the few vendors that profits when you pick someone else's infrastructure, which is worth knowing when you read our ranking. See Nitrosend and Amazon SES compared.
- Amazon SES at a glance
- Verified on the vendor's own pages
- Best for
- high volume where you can absorb the operational work
- Pricing model
- usage
- Free tier
- 3,000 message charges a month for the first 12 months, for new senders
- Entry paid plan
- $0.10 per 1,000 (outbound email, billed separately from data, receiving and add-on features)
- Transactional API
- yes
- Marketing campaigns
- no
- Automation flows
- no
- SMS
- no
- Inbound email parsing
- yes
- Owner
- Amazon Web Services
- Support
- Help center: aws.amazon.com/contact-us
- Developer docs
- API documentation: docs.aws.amazon.com/ses
- Status page
- System status: health.aws.amazon.com/health/status
- Pricing page
- Current pricing: aws.amazon.com/ses/pricing
- Limitations
- No campaign layer and no templates worth using
- No meaningful analytics
- Reputation management is your problem
- Facts checked
5. MailerSend
Best for: teams that want a friendlier SES with a template builder attached.
Solid transactional API, reasonable free tier, decent templates, and a drag-and-drop builder that non-engineers can use. It is a competent middle option that does not win any single criterion and does not fail any either.
Free tier: 3,000 a month. Paid: from $24 a month.
- MailerSend at a glance
- Verified on the vendor's own pages
- Best for
- teams that want a friendlier SES with a template builder attached
- Pricing model
- per send
- Free tier
- 500 emails a month
- Entry paid plan
- $7/mo (5,000 emails a month, 5 seats, 1 domain, 10 templates, 1,000 daily API requests; extra usage $1.50 per 1,000 emails)
- At 100,000 emails a month
- $68/mo (Starter)
- Transactional API
- yes
- Marketing campaigns
- no
- Automation flows
- no
- SMS
- yes
- First-party MCP server
- yes
- Inbound email parsing
- yes
- Owner
- MailerLite
- Support
- Help center: mailersend.com/help
- Developer docs
- API documentation: developers.mailersend.com
- Status page
- System status: status.mailersend.com
- Pricing page
- Current pricing: mailersend.com/pricing
- Limitations
- No marketing campaigns or automation flows
- No MCP server
- Plan volumes are slider-driven rather than published
- Facts checked
6. Loops
Best for: SaaS products that want product email and lifecycle marketing in one tool with minimal setup.
Loops is the closest thing on this list to Nitrosend's shape, in that it deliberately covers both transactional and marketing. It is opinionated and pleasant, priced per contact rather than per send, which is the right model for some businesses and an expensive one for others. No MCP surface. See Nitrosend and Loops compared.
- Loops at a glance
- Verified on the vendor's own pages
- Best for
- SaaS products that want product email and lifecycle marketing in one tool with minimal setup
- Pricing model
- per contact
- Free tier
- 1,000 subscribed contacts, up to 4,000 sends a month
- Entry paid plan
- $49/mo (5,000 subscribers, unlimited sends to subscribers, transactional sends to users outside your audience, all features, no per-seat fee)
- At 10,000 contacts
- $99/mo (Growing Audience Plan)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- no
- Inbound email parsing
- no
- Support
- Help center: loops.so/docs
- Developer docs
- API documentation: loops.so/docs/api-reference
- Status page
- System status: status.loops.so
- Pricing page
- Current pricing: loops.so/pricing
- Limitations
- Priced per contact rather than per send, which is expensive if you store far more than you mail
- No MCP surface
- Facts checked
7. SendGrid
Best for: teams already inside Twilio who want one vendor for SMS, voice and email.
SendGrid is mature, enormous, and will not fall over. The problem is structural: transactional and marketing are two separate products that happen to share a login, so the integration between them is awkward in exactly the way the third criterion is meant to catch. Shared IP pools mean your reputation is partly a function of other people's sending habits.
Free tier: 100 a day. Paid: from $19.95 a month for 50,000. See Nitrosend and SendGrid compared.
- SendGrid at a glance
- Verified on the vendor's own pages
- Best for
- teams already inside Twilio who want one vendor for SMS, voice and email
- Pricing model
- hybrid
- Free tier
- 60-day free trial, 100 emails a day, no credit card
- Entry paid plan
- $19.95/mo (50,000 emails a month, Email API, analytics and deliverability tooling; taxes and overages extra)
- At 100,000 emails a month
- $34.95/mo (Essentials 100k)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- yes
- SMS
- no
- Inbound email parsing
- yes
- Owner
- Twilio
- Support
- Help center: support.sendgrid.com
- Developer docs
- API documentation: twilio.com/docs/sendgrid
- Status page
- System status: status.sendgrid.com
- Pricing page
- Current pricing: twilio.com/en-us/products/email-api/pricing
- Limitations
- Transactional and marketing are two separate products sharing a login
- Shared IP pools tie your reputation to other senders
- The free tier is capped at 100 emails a day
- Facts checked
8. Mailgun
Best for: transactional workloads where routing and inbound handling matter as much as sending.
Strong API, mature webhooks, flexible routing rules, and real inbound email support, which is something Nitrosend does not offer at all. If your application needs to receive and parse email, Mailgun is on this list and we are not a candidate. Marketing features are limited. See Nitrosend and Mailgun compared.
- Mailgun at a glance
- Verified on the vendor's own pages
- Best for
- transactional workloads where routing and inbound handling matter as much as sending
- Pricing model
- per send
- Free tier
- 100 emails a day
- Entry paid plan
- $15/mo (included monthly emails, overage from $1.80 per 1,000)
- Transactional API
- yes
- Marketing campaigns
- yes
- Automation flows
- no
- SMS
- no
- Inbound email parsing
- yes
- Owner
- Sinch
- Support
- Help center: help.mailgun.com
- Developer docs
- API documentation: documentation.mailgun.com
- Status page
- System status: status.mailgun.com
- Pricing page
- Current pricing: mailgun.com/pricing
- Limitations
- Marketing features are limited
- Trial only, with no perpetual free tier
- Facts checked
What actually separates them
After fifteen years of this, three things predict whether you will still be happy in a year.
The streams. Cold outreach infrastructure is not marketing email is not transactional email. Different domains, different mailboxes, different volumes, different deliverability rules. Providers that pretend these are one problem create incidents. Providers that force you into two vendors create seams. Look for one account that separates streams internally.
The migration cost, which nobody quotes. We ported email across to an existing tool about a year ago. It was hours of setup, then weeks of warming up and optimisation, and it became a three-month project on a large platform. That cost is invisible on every pricing page on this list. Weight it accordingly, and check how to warm up an email domain before you commit to a move.
How it behaves under load. Throughput, queueing and the ramp a new sender is held to are covered on best email sending API, and they decide whether your first big campaign goes out at all.
Whether an agent can drive it. This is the newest criterion and the one the category has not caught up on. Traditional email APIs like SendGrid, Mailgun and Postmark are reliable, and they are built on infrastructure that predates any of this. The gap between what AI can do and what email platforms let you do with it is enormous, and it is currently the most useful thing to be picky about. Our own MCP usage is already maturing past chat: the first productised MCP client we saw, gather-app/1.0, polls every fifteen minutes rather than waiting for a human to type.
One warning if you are leaning on an assistant to pick for you. AI does not actually know email marketing. It confidently makes things up, from generic unsourced welcome sequences to hallucinations about deliverability. Ask it for the mechanism, not the recommendation.
FAQ
What is the best email API for most teams?
For teams that will need both transactional and marketing email, Nitrosend, because it covers both from one account with a full agent surface. For transactional-only workloads where deliverability is the entire job, Postmark. For the lowest possible unit cost at high volume, Amazon SES.
Is there a genuinely free email API?
Yes, several. Nitrosend gives 8,000 emails then 500 a month with full API, MCP and CLI access. Resend gives 3,000 a month and MailerSend 3,000. Free tiers are compared in detail on the best free email API page.
Should I use SMTP or the HTTP API?
Use the HTTP API for anything new. It returns structured errors, avoids connection overhead and is easier to debug. Keep SMTP for legacy systems that cannot speak HTTP. The tradeoffs are covered on SMTP vs API email services.
Which email API works with AI agents?
Nitrosend and Resend are the only two here with a first-party MCP server. Resend's is send-focused. Nitrosend exposes 28 tools covering campaigns, contacts, flows and billing. See best email API for AI agents.
Does this list rank Nitrosend first because you make it?
We make it, and it is ranked first against published weights you can disagree with. The weights are above, the losses are named in each entry, and the fact that we support running competitors' infrastructure underneath us is the reason we can afford to be specific. If your job is transactional-only at the lowest cost, this list tells you to use SES.