Email APIs for AI agents: sending and inboxes
Transactional email APIs an agent can send through, and agent inboxes that also receive and reply.
5 tools, listed alphabetically. Prices and features checked 2026-10-17 on each vendor's own pages; “not verified” means we could not confirm it.
Short answer: For sending, Resend has the most generous free plan here (3,000 emails/month) and Pro at $20/month for 50,000. Postmark and Mailgun start at $15/month for 10,000 emails, and SendGrid's Essentials starts at $19.95/month after a 60-day trial. If the agent must receive and answer email in its own mailbox, AgentMail is built for that: free for 3 inboxes, $20/month for 10.
| Tool | Free tier | Entry paid price | Meter | MCP server | Open source | Receives email |
|---|---|---|---|---|---|---|
| AgentMail | Free: 3 inboxes, 3,000 emails/month (100/day), 3 GB [source, checked 2026-10-17] | Developer $20/month: 10 inboxes, 10,000 emails, 10 custom domains; Startup $200/month: 150 inboxes; add-ons $2 per inbox, domain or 1,000 emails [source, checked 2026-10-17] | Inboxes, emails per month and storage; add-ons per inbox, domain or 1,000 emails [source] | MCP server (OAuth or API key) [source] | not verified | Yes: every inbox sends and receives, with threads [source] |
| Mailgun | Free: 100 emails/day, 1 custom sending domain [source, checked 2026-10-17] | Basic from $15/month: 10,000 emails ($1.80 per extra 1,000); Foundation $35/month: 50,000; Scale $90/month: 100,000 [source, checked 2026-10-17] | Emails per month; extra messages per 1,000, tiered by plan [source] | Official MCP server (Apache-2.0) [source] | not verified | not verified |
| Postmark | Developer: 100 emails/month, no overages, does not expire [source, checked 2026-10-17] | Basic $15/month: 10,000 emails, then $1.80 per 1,000; Pro $16.50 ($1.30 per 1,000); Platform $18 ($1.20 per 1,000) [source, checked 2026-10-17] | Emails per month; extra emails per 1,000 [source] | Official MCP server by ActiveCampaign (MIT) [source] | not verified | not verified |
| Resend | Free: 3,000 emails/month, 100/day, 3 domains [source, checked 2026-10-17] | Pro $20/month: 50,000 emails, then $0.90 per 1,000; Scale $90/month: 100,000 emails [source, checked 2026-10-17] | Emails per month; overage billed per 1,000 at the plan's rate [source] | Official MCP server (MIT) [source] | not verified | not verified |
| Twilio SendGrid | 60-day free trial: 100 emails/day, no credit card [source, checked 2026-10-17] | Essentials from $19.95/month; Pro from $89.95/month (dedicated IPs); Premier custom [source, checked 2026-10-17] | Monthly email volume and plan features [source] | not verified | not verified | not verified |
| Tool | Best for | Compliance | Data retention |
|---|---|---|---|
| AgentMail | Agents that need their own inbox to receive, read and reply to email, not just send. | SOC 2 report on Startup and Enterprise [source] | not verified |
| Mailgun | Senders who want a permanent free tier for testing and published volume rates down to $0.40 per 1,000. | not verified | Logs: 1 day on Free and Basic, 5 days on Foundation, 30 days on Scale [source] |
| Postmark | Transactional email where you want separate message streams, published overage rates and longer log retention. | not verified | 45 days on Basic; customizable up to 365 days on Pro and Platform [source] |
| Resend | Developers sending transactional email from code who want a usable free tier, React Email and an official MCP server. | SOC 2 Type II and GDPR listed on every plan [source] | 30 days of data on Free [source] |
| Twilio SendGrid | High-volume senders who also want Twilio's other channels on the same account. | SOC 2 Type II certification listed [source] | not verified |
What to check before you pick one
- Send only or two-way: AgentMail gives each agent an inbox with threads; the others are mainly sending services with inbound routing.
- Free allowance: Resend 3,000/month, AgentMail 3,000/month, Mailgun 100/day, Postmark 100/month, SendGrid 100/day for 60 days only.
- Overage rate: Resend $0.90, Postmark $1.20–1.80 and Mailgun from $1.80 down to $0.40 per 1,000, depending on plan and volume.
- Log retention: Mailgun keeps logs for 1 day on Free and Basic; Postmark keeps 45 days by default.
- MCP: Resend, Postmark, Mailgun and AgentMail have official MCP servers; we did not find one for SendGrid.
FAQ
Can an AI agent have its own email address?
Yes. AgentMail creates inboxes through its API, and each can send, receive and keep threads. Resend's pricing page also lists inboxes. A plain sending API (Postmark, Mailgun, SendGrid) sends from your domain, and replies need inbound routing that you set up.
What is the cheapest email API for an agent?
At low volume, Resend Free (3,000 emails/month) and AgentMail Free (3 inboxes, 3,000 emails/month) cost nothing. At 50,000 emails a month, Resend Pro is $20 and Mailgun Foundation is $35, on list prices checked 17 Oct 2026.
Should an agent send marketing email?
Check each provider's acceptable-use policy and keep transactional and bulk mail apart. Postmark separates them with message streams.
Comparisons and alternatives
Other categories: Social posting · Payments · Phone, SMS and voice · Browser automation · Web search and scraping