Replyz / Alternatives / Best email APIs for AI agents
Best email APIs for AI agents: inbox APIs vs sending APIs.
"Email API" covers two different things. Sending APIs deliver mail from your app. Inbox APIs give an agent an address of its own that it can receive at, read and reply from. Most agent jobs (sign-ups, verification codes, supplier email) need the second kind. We make Replyz, so it's in the list; facts about the others come from their own pages, checked on 6 November 2026.
Inbox API or sending API?
| Agent inbox API | Sending API | |
|---|---|---|
| Gives the agent an address to receive at | Yes, one per agent or task | No (some add inbound webhooks for your domain) |
| Agent can wait for a reply or code | Usually, through MCP, a CLI or the API | You build it |
| Built for | Agents that sign up, read and reply | Apps that send notifications |
Agent inbox APIs compared
| Entry price | Inboxes | EU hosting | Stand-out | |
|---|---|---|---|---|
| Replyz | 19 € / month (planned) | 100 | Every plan | Wait and code extraction built in; for personal agents |
| AgentMail | $20 / month | 10 | Enterprise only | Category leader, live today |
| Dead Simple Email | $29 / month | 100 | Not stated | IMAP/SMTP on every inbox |
| Nylas agent accounts | $15 / month | 10 | US or EU, every plan | Calendar included |
| Resend Inboxes | $1 per extra inbox | 3 per plan | Not stated | Same account as Resend sending |
Sources: replyz.io (planned prices), agentmail.to/pricing, deadsimple.email, nylas.com/pricing and resend.com/pricing, checked on 6 November 2026. Detailed comparisons: AgentMail, Dead Simple Email, Nylas, Resend Inboxes.
What to check before you choose
- One inbox per agent or task. Keeps sign-ups and conversations apart, and makes the price per inbox matter.
- How the agent waits for mail. A call that waits for the next message is simpler for an agent than consuming webhooks or a stream.
- Code and link extraction. Verification codes are the most common reason an agent needs email. Built-in extraction saves a parser.
- How the agent connects. A skill and CLI for agents on your machine (Claude Code, OpenClaw, Hermes), an MCP server for agents in an app (Claude, Cursor). See all agents.
- Where data lives. If you or your users are in Europe, check the hosting region on the plan you'd actually buy.
- Sending rules. Who the agent may email, and whether you approve before it sends.
When a sending API is enough
If your agent only sends notifications from your own domain and never needs to receive, a transactional sending API is simpler and cheaper. Once it needs to sign up for something, read a code or handle a reply, it needs an inbox.
Frequently asked questions
What is the best email API for AI agents?
It depends on the job. If the agent needs its own address to sign up, receive codes and reply, use an agent inbox API such as Replyz, AgentMail, Dead Simple Email, Nylas agent accounts or Resend Inboxes. If it only sends notifications, a sending API is enough.
What's the difference between an inbox API and a sending API?
A sending API delivers email from your app. An inbox API gives each agent an address it can receive at, read and reply from, usually with an MCP server or CLI so the agent can use it directly.
What should I check before choosing an email API for an agent?
Whether each agent gets its own inbox, how the agent waits for new mail, whether verification codes are extracted for it, which agents it connects to (MCP, CLI, skill), where data is hosted, and the price per inbox.
Which email API for agents is hosted in the EU?
Replyz stores mail in the EU on every plan. Nylas offers US or EU hosting on every plan. AgentMail lists an EU region on its Enterprise plan.