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

TL;DR

• Nine permanent free tiers still matter in 2026: Resend, Sendkit, Sequenzy, Mailgun, Postmark, Mailtrap, MailSlurp, Mermail, and Cloudflare Email Routing.
• Daily caps bite first: Mermail Free is 100 emails/day per mailbox; Resend and Mailgun sit at 100/day; Mailtrap shares 150/day.
• Inbound on free splits webhook routes (Resend, Mailgun, Mailtrap, Cloudflare) vs stored inboxes (Mermail; MailSlurp for tests).
• SES has no permanent free send quota on the current pricing page; inbound.new still markets free webhooks while live pricing often starts paid.
• Mermail Free keeps 1 persistent agent inbox (send + receive + threads + MCP) at 1,000 emails/month, 100/day, 1 GB — built for agents that need identity, not just a send meter.

Eleven free email API plans teams actually use in 2026 are Mermail, 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 Mermail fit depending on whether you need a one-shot webhook fire or a stored, queryable inbox your agent can own.

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 generous free webhook copy on its product page while live pricing often starts at a paid Default plan — verify before you design around it.

Mermail Free is the persistent-inbox row for agents: 1 real inbox, 1,000 emails/month, 100/day per mailbox, 1 GB storage, MCP included, Mermail-hosted domain, no custom domains on Free. When you need more inboxes, custom domains, and production quotas, Developer starts at $19/mo ($1 first month on the early-adopter offer).

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, Mermail, 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: product marketing may still say free webhooks, while the pricing page lists a paid Default plan. Treat that as "verify live checkout," not as a guaranteed free forever allotment.

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 short log retention. Resend Free matches the 100/day rhythm many builders feel, but stores inbound as webhook events rather than a queryable agent inbox. Treat "free forever" as a product claim you re-check 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: monthly volume, daily caps, inbound shape, inbox count, retention, and what the free tier is best for. Competitor numbers were checked against public pricing pages in late August 2026; Mermail Free numbers match mermail.app/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 monthly and daily 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. Mermail Free receives into a persistent inbox you can list, thread, search, and drive through MCP — the difference between "a POST fired once" and "my agent can reopen last week's conversation."

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.

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 yourself. That gap is why "email API" and "inbox API" are different jobs for AI agents.

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, Mermail 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. Do not plan production volume on credits that end after the Free Tier window.

Also watch "free for 1 month" promotions on paid tiers from other vendors. Those are paid-plan trials, not the permanent free plan. When a competitor page still cites an old SES "62,000 from EC2" line, check the live SES pricing page yourself.

Why 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 about shared send+receive. Mermail Free likewise budgets emails across the inbox workload — a support-style loop that sends a confirmation and then receives three customer replies can burn multiple 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 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

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.

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

Mermail Free is the row that keeps a real inbox with send, receive, threads, drafts, and MCP tools under one plan. That is the difference between "email arrived at my webhook once" and "my agent can list last week's thread, extract an OTP safely, and keep the receipt." AgentMail is another inbox-first option worth knowing; Mermail's differentiator on Free is the agent-native surface — MCP, privacy-first storage, and a path to Agent Wallet on OAuth when you leave the free ceiling.

How Mermail's free tier compares for persistent inboxes

Mermail Free is built around an agent-owned inbox, not around a send meter alone. Per mermail.app/pricing, Free includes 1 inbox, 1,000 emails/month, 100 emails/day per mailbox, 1 GB storage, MCP server access, websockets, drafts, schedule send, and community support — with no credit card required. Custom domains are not part of Free; they start on Developer ($19/mo, with a $1 first-month early-adopter offer) alongside 5 inboxes and 10,000 emails/month.

Compared with Resend Free, you trade React-oriented send DX and a higher monthly send allotment for stored messages you can query, thread, and expose to an agent through typed MCP tools.

Compared with Mailtrap Free, you get fewer monthly emails (1,000 vs 4,000) and a tighter shared feel on volume, but the unit of account is an inbox with threads rather than a short log window.

Compared with MailSlurp Free, Mermail allows real external send within plan limits instead of sandbox-only egress — so the same inbox can finish a signup loop, not just a test assertion.

Compared with other agent-inbox products, Mermail's Free tier is intentionally lean on inbox count (1) while shipping the agent control plane: MCP profiles (including least-privilege agent-inbox), privacy-first storage, and a clear upgrade path to wallet-enabled OAuth workflows.

Smoke-test Mermail Free with MCP

Connect the hosted MCP server, then ask your agent to create or list a mailbox. Success looks like: MCP connected, list_mailboxes returns your Free inbox, and a test send/receive lands in the same thread.

# Add Mermail MCP (API key header) — or use OAuth in hosts that support it
# URL: https://console.mermail.app/mcp
# Header: x-api-key: <your workspace key>

# Least-privilege read/verify profile for OTP-style workflows:
# https://console.mermail.app/mcp?profile=agent-inbox

# In your agent session, ask:
# 1) "List my Mermail mailboxes"
# 2) "Create a mailbox called free-tier-smoke-test"
# 3) "Send a test email to me from that mailbox, then list new messages"

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 (Mermail Free has none; Resend Free lists a small domain allotment; Sendkit Free lists 1). Log retention on Mailgun Free is measured in days, not months. 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/storage is too short for disputes or agent memory, or you need more than a single inbox.

Mermail's next step is Developer at $19/mo (5 inboxes, 10,000 emails/month, 100/day per mailbox, custom domains, higher API and AI quotas), with a $1 first-month early-adopter path for eligible accounts. Resend and Mailtrap move you to paid volume tiers when 100–150 emails/day is not enough.

SES becomes rational when monthly volume makes per-thousand pricing cheaper than SaaS included tiers and your team already runs AWS. If an "inbound-only" vendor's checkout is already paid, treat that as your floor — not the marketing free line.

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.

Bottom line

If you only need to send receipts, pick a send-first free tier and move on. If your agent needs to own an address, keep threads, receive OTPs, and operate through MCP without borrowing someone's Gmail — start on Mermail Free, then graduate when you need more inboxes and your own domain.

Mermail gives your agents real inboxes — and a path to a user-controlled Agent Wallet when the workflow has to pay. Create an inbox, connect MCP, send and receive with zero SMTP theater. Free to start.

FAQ

Which free email APIs are permanent in 2026?

Resend, Sendkit, Sequenzy, Mailgun, Postmark, Mailtrap, MailSlurp, Mermail, and Cloudflare Email Routing publish ongoing free plans or free forwarding with caps. Amazon SES on the current pricing page is pay as you go without a permanent free send quota. Always re-check inbound-first vendors whose product page and pricing page disagree.

Which free tiers include inbound webhooks?

Resend inbound, Mailgun Free with one inbound route, Mailtrap Email API Free, Cloudflare Email Routing with Email Workers, Mermail Free inboxes, and MailSlurp Free test inboxes all support inbound paths. Postmark Free does not include Inbound Email.

Why do daily caps matter more than monthly free limits?

Burst traffic hits daily caps first. Mermail Free lists 100 emails per day per mailbox; Resend Free lists 100/day; Mailtrap Free lists 150/day shared across send and receive. A launch-week retry storm can exhaust the day while the monthly counter still looks fine.

Does Amazon SES still offer free emails from EC2?

The SES pricing page in 2026 lists pay-as-you-go plans and AWS Free Tier credits for new customers. It does not document a permanent free monthly send quota. Do not plan on an old EC2-only free allotment unless AWS still states it on the live pricing page.

How does Mermail Free compare for persistent inboxes?

Mermail Free includes 1 inbox, 1,000 emails per month, 100 emails per day per mailbox, and 1 GB storage with send and receive in the same plan — plus MCP. Custom domains are not on Free and start on Developer. It fits prototypes that need stored threads and agent tooling rather than webhook-only inbound.