Email API Free Tiers Compared

Command references used in this guide: nylas init, nylas auth list, and nylas email send.

What does each email API free tier include?

Six email APIs offer a usable free tier in June 2026: SendGrid sends 100 emails/day for 60 days, Mailgun 100/day, Postmark 100/month, Resend 3,000/month, Brevo 300/day, and Nylas runs a full-access sandbox metered by connected accounts instead of messages. Every email API free tier claim in this table links the provider's live pricing page.

The caps aren't directly comparable because the products aren't. The first five are transactional senders: they push mail from your domain and never read an inbox. Nylas connects to mailboxes users already have, so its sandbox is measured in accounts rather than messages. The email API comparison guide covers that product split; this page sticks to what $0 buys you at each vendor.

Which email API free tiers expire or need a credit card?

Only SendGrid's free tier expires. Its plan page states the Free Trial “covers storage of 100 contacts and sending 100 emails each day for 60 days.” The Mailgun, Postmark, Resend, Brevo, and Nylas free tiers run indefinitely, and four of the six vendors state outright that no credit card is required to start.

The no-card claims come from the vendors themselves. Postmark's pricing FAQ says of its free developer plan: “Use it for however long you need, it doesn't expire.” Brevo's pricing page labels its plan “Free forever, no credit card needed.” The Nylas pricing FAQ answers the same question with “no credit card required.” SendGrid's page also waives the card, but the 60-day clock starts at signup — after it runs out, the cheapest paid plan (Essentials) starts at $19.95/month. If you're budgeting past the free stage, the pricing models guide works the math at 5, 100, and 1,000 accounts.

What sandbox restrictions hide inside free email API tiers?

Send caps are the visible limit; the quieter restrictions cost more debugging time. Mailgun's free plan keeps logs for 1 day. Postmark's allows no overages, so message 101 in a month is rejected. Resend's free plan permits 1 custom domain and 1 webhook endpoint. Brevo stamps its footer on every free-plan email.

• Mailgun — 1-day log retention, 2 API keys, and 1 custom sending domain. Paid Basic ($15/month for 10,000 emails) lifts the daily cap.
• Postmark — the plan card says “No overages allowed in this plan,” a hard stop rather than a surprise invoice. Basic is $15/month for 10,000 emails.
• Resend — the 3,000/month allowance carries a 100/day sub-limit, 30-day data retention, and a single webhook endpoint.
• Brevo — removing the “Sent with Brevo” footer is a paid Starter feature, and sending begins only after Brevo approves your account.
• SendGrid — the trial caps contact storage at 100, which rules out testing list-based sends at any realistic size.

Here's the surprise promised up top: the restriction that bites hardest isn't a send cap, it's Mailgun's 1-day log window. Deliverability problems surface over days, and when yesterday's bounce records are already gone, you debug blind. A 100-email cap slows a test; missing logs invalidate it.

How do I test the Nylas free sandbox from the terminal?

The Nylas free sandbox connects up to 5 real mailboxes with what the pricing FAQ calls “full API access to test email, calendar, scheduling, and notetaking,” and no credit card. From the terminal, the CLI goes from install to a sent message in about 2 minutes, with no server to deploy and no DNS records to set.

Install with Homebrew (other methods are in the getting started guide), then run nylas init. The wizard walks through 4 steps: creating or logging into an account, selecting an application, activating an API key, and syncing your first mailbox. After that, one command sends a real message through the sandbox.

# Install the CLI
brew install nylas/nylas-cli/nylas

# Guided sandbox setup: account, app, API key, first mailbox
nylas init

# Confirm which accounts are connected (up to 5 free)
nylas auth list

# Send a real message through the free sandbox
nylas email send --to you@example.com \
  --subject "Sandbox test" \
  --body "Sent from the Nylas free tier" --yes

When a project outgrows the sandbox, nylas auth list doubles as a billing forecast: the Full Platform plan is $15/month including 5 connected accounts, then $2 per additional account. Unlike the send-only tiers above, the account count is the only number that moves the bill.

Which email API free tier fits which project?

Match the email API free tier to what you're actually testing. Evaluating transactional deliverability points to Postmark's never-expiring 100/month. A side project under 3,000 sends a month fits Resend. Marketing campaigns fit Brevo's 300/day. Reading inboxes, syncing calendars, or building an agent fits the Nylas sandbox — the only tier here that isn't send-only.

Two more deciding factors. First, ownership: SendGrid has been part of Twilio since the acquisition completed in February 2019, so its free trial is the on-ramp to the wider Twilio platform — the Twilio vs Nylas comparison weighs that bundle against a mailbox-first API. Second, hosting: if the appeal of $0 is really about avoiding a vendor, a self-hosted gateway changes the trade entirely, which the EmailEngine vs Nylas guide covers. For teams choosing a tier they'll grow out of in 6 months, free-tier generosity matters less than what month 7 costs.

Next steps

• High-Volume Email APIs Compared — SendGrid, Mailgun, and Amazon SES vs contextual email APIs
• Email API pricing models — what happens to each of these tiers when you start paying
• Best email API for developers — the full vendor comparison beyond the free tier
• Email API for SaaS startups — picking a tier you won't have to migrate off
• Twilio vs Nylas — the platform behind SendGrid, head to head
• EmailEngine vs Nylas — the self-hosted route when $0 means no vendor at all
• Getting started — install the CLI and connect your first sandbox account
• Full command reference — every flag and subcommand documented