11 Free Email APIs Compared: Send Limits, Inbound, and Retention (2026)

Eleven free email API plans teams actually use in 2026 are AgentMail, Resend, Mailgun, MailSlurp, Sequenzy, Sendkit, inbound.new, Mailtrap, Cloudflare Email Workers, Amazon SES, and Postmark. The useful free tiers are permanent plans with clear daily or monthly caps, not expired trials. For send-only transactional mail, Resend (3,000/mo, 100/day), Sendkit (3,000/mo), Sequenzy (2,500/mo), Mailgun (100/day), and Postmark (100/mo) are the usual picks.

For inbound webhooks, Resend, Mailgun (1 free inbound route), Mailtrap (shared send/receive), Cloudflare Email Routing plus Workers, and AgentMail fit depending on whether you need a webhook fire or a stored inbox. MailSlurp free is a test sandbox (external send blocked). Amazon SES on the current pricing page is pay as you go with no permanent free send quota listed. inbound.new still markets 1,000 webhooks/mo free on its product page while live pricing starts at Default $4/mo.

AgentMail free is the persistent-inbox row: 3 inboxes, 3,000 emails/month, 100/day, 3 GB, no custom domains on Free. For a capability best-of beyond free limits, see 6 Best Email API For Developers Compared.

Which email APIs have a permanent free tier in 2026?

Nine of the eleven providers in this roundup publish a permanent $0 plan or free forwarding that does not expire on a calendar trial. Resend, Sendkit, Sequenzy, Mailgun, Postmark, Mailtrap Email API, MailSlurp, AgentMail, and Cloudflare Email Routing all document ongoing free usage with hard caps. Amazon SES is pay as you go on the current pricing page, so it is in the table for startup cost context, not as a permanent free send allotment.

inbound.new is the ambiguous row: the email webhook product page still says 1,000 webhooks/month free, while the pricing page lists Default at $4/mo for 5,000 emails with no free plan card.

Permanent free is not the same as generous. Postmark Free is 100 emails/month forever. Mailgun Free is 100 emails/day with 1 inbound route and 1 day of log retention. Resend Free matches AgentMail on the 100/day rhythm but stores inbound as webhook events rather than a queryable inbox. Treat "free forever" as a product claim you verify on the vendor pricing URL the week you ship.

Free email API limits table (send, receive, inboxes, daily caps, retention)

The table below is the decision surface for this page: monthly volume, daily caps, inbound shape, inbox count, retention, and what the free tier is best for. Numbers were checked on vendor pricing pages on 2026-08-27.

Sources: agentmail.to/pricing, resend.com/pricing, mailgun.com/pricing, mailslurp.com/pricing, sequenzy.com, sendkit.dev/en, inbound.new/pricing.

Sources: inbound.new/email-webhook-api, mailtrap.io/pricing, cloudflare.com Email Routing, cloudflare.com Workers Free, aws.amazon.com/ses/pricing, postmarkapp.com/pricing.

Which free tiers include inbound webhooks

Inbound on a free plan is the filter most listicles skip. Resend documents inbound email on all plans, including Free, as webhook delivery rather than a hosted mailbox. Mailgun Free includes 1 inbound route. Mailtrap Email API Free includes inbound and shares the 4,000/mo and 150/day quotas with outbound.

Cloudflare Email Routing is free for custom addresses and forwarding, and Email Workers let you run custom logic on inbound messages inside the Workers Free request budget (100,000 requests/day, 10ms CPU per request on Free). AgentMail Free receives into persistent inboxes you can list, thread, and webhook. MailSlurp Free receives into a reusable test inbox with webhooks, with external send blocked. Postmark Free does not include Inbound Email; that sits on Platform.

Sequenzy and Sendkit free tiers are positioned around outbound transactional and lifecycle mail. Amazon SES can receive through receipt rules, but that is billed infrastructure you assemble, not a free inbox product. inbound.new is inbound-first; confirm whether you are on the marketed free webhook allotment or the $4 Default plan before you design around it.

If the product needs conversation history, not only a POST body, prefer a provider that stores messages. Webhook-only free tiers force you to build storage, idempotency, and threading. That gap is why Email API vs Inbox API and Best Email APIs for Receiving and Parsing Replies exist as companion pages.

Trial vs permanent free: what expires

A permanent free tier keeps the same caps every month until the vendor changes the plan. Resend Free, Sendkit Free, Sequenzy Free, Mailgun Free, Postmark Free Developer, Mailtrap Free, MailSlurp Free, AgentMail Free, and Cloudflare Email Routing fit that pattern based on their public pricing pages. A trial burns a clock or a one-time credit pile and then forces a card.

Amazon SES currently points new AWS customers at Free Tier credits usable across eligible services, including SES, rather than a lasting SES-only free send allotment on the SES pricing page. Do not plan production volume on credits that end after the Free Tier window.

Also watch "Foundation free for 1 month" style promotions on paid Mailgun tiers. Those are paid-plan trials, not the Mailgun Free plan with 100 emails/day. When a competitor page still cites an old SES "62,000 from EC2" line, check aws.amazon.com/ses/pricing yourself. The page retrieved for this draft lists pay-as-you-go plans and Free Tier credits, not a permanent free monthly send quota.

Why do shared send and receive quotas run out faster?

Shared quotas count every outbound notification and every inbound reply against one monthly or daily bucket. Mailtrap Free is explicit: 4,000 emails/month and 150/day are shared across sending and receiving. AgentMail Free likewise budgets 3,000 emails/month and 100/day across the inbox workload, not a separate receive pool. A support agent that sends a confirmation and then receives three customer replies can burn four units for one conversation.

Send-only free tiers (Resend outbound, Sendkit, Sequenzy, Postmark Free) feel larger until you bolt on a second inbound product and discover two billing systems.

Daily caps bite earlier than monthly caps for bursty agent traffic. One hundred emails/day on Resend or AgentMail is about three thousand a month if you are perfectly even, which real products are not. A Monday deploy that retries webhooks or backfills password resets can exhaust the day while the monthly counter still looks healthy. Design retries and fan-out with the daily number on a sticky note.

Best free email API by job (send-only, inbound webhook, test inboxes, agent inboxes)

Pick by the job, not by the biggest monthly number on a homepage.

Send-only transactional. Resend Free (3,000/mo, 100/day) and Sendkit Free (3,000/mo, 1 domain) are the clean permanent free send APIs. Sequenzy Free (2,500/mo) fits if you also want lifecycle sequences in the same product. Postmark Free (100/mo) is only for a tiny always-on smoke test. Mailgun Free (100/day) works for low-volume routing tests.

Inbound webhook without owning a mailbox. Cloudflare Email Routing plus Email Workers, Resend inbound, Mailgun's one free inbound route, and Mailtrap inbound are the free-path options. inbound.new is inbound-native; re-read pricing the day you integrate because the product page and pricing page disagree on free versus $4 Default.

Test inboxes. MailSlurp Free is built for creating and receiving in a sandbox with external send blocked. Use it for E2E signup tests, not for customer email.

Agent or product inboxes that must persist. AgentMail Free is the row that keeps three real inboxes with send, receive, threads, and storage under one plan. That is the difference between "email arrived at my webhook once" and "my agent can list last week's thread." For framework wiring after you leave free, the email for AI agents guide covers architecture beyond limits.

How does AgentMail's free tier compare for persistent inboxes?

AgentMail Free is built around inboxes, not around a send meter alone. Per agentmail.to/pricing on 2026-08-27, Free includes 3 inboxes, 3,000 emails/month, 100 emails/day, 3 GB storage, and no credit card. Custom domains are not part of Free; they start on Developer ($20/mo) with 10 custom domains on that plan card. Compared with Resend Free, you trade React-oriented send DX for stored messages you can query.

Compared with Mailtrap Free, you get fewer monthly emails (3,000 vs 4,000) and a tighter daily cap (100 vs 150), but the unit of account is an inbox with threading rather than a short log window (Mailtrap Free keeps 3 days of logs). Compared with MailSlurp Free, AgentMail allows external send within plan limits instead of sandbox-only egress.

Create an inbox and send on Free with the Node SDK (signatures from the AgentMail Node reference). https://github.com/agentmail-to/agentmail-node/blob/main/reference.md

import { AgentMailClient } from "agentmail";

const client = new AgentMailClient({ apiKey: process.env.AGENTMAIL_API_KEY });

const inbox = await client.inboxes.create({});
const sent = await client.inboxes.messages.send(inbox.inboxId, {
  to: ["you@example.com"],
  subject: "Free tier smoke test",
  text: "Sent from an AgentMail free inbox",
});
console.log(inbox.inboxId, sent.messageId);

List what arrived without standing up your own store. https://github.com/agentmail-to/agentmail-node/blob/main/reference.md

const page = await client.inboxes.messages.list(inbox.inboxId);
for (const msg of page.messages ?? []) {
  console.log(msg.from, msg.subject);
}

The honest limit for this use: three inboxes is enough for a prototype agent and two fixtures, not a multi-tenant fleet. When each customer needs an isolated mailbox and a custom domain, Free is the wrong plan by design.

Limitations: what no free tier gives you

No free email API in this table gives you unlimited daily burst, long forensic retention, dedicated IPs, and multi-tenant isolation at once. Free tiers omit or tightly ration custom domains (AgentMail Free has none; Resend Free lists 3 domains; Sendkit Free lists 1). Log retention on Mailgun Free is 1 day; Mailtrap Free is 3 days. Postmark Free excludes inbound.

MailSlurp Free blocks external send. Cloudflare Email Routing forwards or runs Workers code; it is not a hosted agent mailbox with threads. SES gives low unit price only after you accept IAM, sandbox exit, and your own storage wiring. Shared send/receive caps mean support-style reply volume collapses the same budget you wanted for outbound receipts.

If a sales page promises "free inbound" without stating route count, retention, and whether messages are stored, assume webhook-only until the docs show a list messages API.

When to leave free and what usually forces the upgrade

Leave free when one of these trips first: the daily cap blocks a real launch week, you need custom domains for production From addresses, retention is too short for disputes or agent memory, or you need more than a handful of inboxes. AgentMail's next step is Developer at $20/mo (10 inboxes, 10,000 emails/month, 1,000/day, custom domains). Resend and Mailtrap move you to paid volume tiers when 100 to 150 emails/day is not enough.

SES becomes rational when monthly volume makes $0.10 to $0.16 per 1,000 emails cheaper than SaaS included tiers and your team already runs AWS. inbound.new's Default $4/mo is already a paid floor if the marketed free webhook allotment is not what checkout gives you.

Free email API choice in 2026 is a limits problem. Rank providers by permanent versus trial, daily caps, shared quotas, inbound shape, inbox count, and retention. Then pick the free row that matches the job you are actually shipping.