InboxAPI

Why not just give my agent access to my Gmail or Outlook?

Security — Gmail/Outlook OAuth gives your agent access to your entire inbox (medical, financial, legal, personal). A prompt injection in any inbound email could manipulate an agent with access to all of it. InboxAPI gives your agent its own isolated inbox with trust classification and datamarking on every message.Identity — When your agent sends from your Gmail, recipients can't tell who they're talking to. Replies go to your inbox, mixed with your real mail. InboxAPI gives your agent its own personal address — clear separation between you and your agent.Practicality — Gmail/Outlook APIs aren'

How is this different from AWS SES, SendGrid, or Resend?

Those are sending APIs — you build email infrastructure on top of them. InboxAPI gives your agent a complete email identity: send, receive, search, reply, and forward. There's nothing to configure and no infrastructure to manage.

How is this different from AgentMail or a1base?

We built our own email stack from the ground up. We don't wrap SES, Postfix, or any third-party sending service. Your agent's mail goes through infrastructure we operate directly.

Is it really free?

Yes. No credit card, no trial period, no usage tiers. We're working on paid plans with additional features, but the core experience will always be free.

What are the current limitations?

While InboxAPI is fully functional, there are a few current limitations:5 external recipient addressbook slots per account (LRU eviction after 5 days of inactivity)It is for agent personal use only, not a transactional service for bulk sending, marketing, or application notifications

How do you prevent spam and abuse?

Account creation requires proof-of-work. Each account has 5 addressbook slots for external recipients — when all slots are in use, the least recently used entry is auto-replaced after 5 days of inactivity. Daily send quotas and rate limiting are enforced on every account. These constraints are structural — they're not policies, they're how the system works.

Do I need to add contacts or configure an addressbook?

No. The addressbook is automatic — contacts are added when your agent sends email. There is no contact list to manage, no settings file to edit, and no configuration step. Each account can send to up to 5 unique external addresses. When all slots are in use, the least recently used entry is auto-replaced after 5 days of inactivity. Emails between InboxAPI agents are always unlimited.

What about prompt injection via email?

Every inbound email includes a trust classification — trusted, agent, unverified, or suspicious — based on whether the sender is in your addressbook and whether their email passes authentication checks. This helps your agent decide how cautiously to handle each message. Emails from other InboxAPI agents are flagged separately so your agent knows to check with you before acting on them. Untrusted email content is also automatically transformed with marker characters (datamarking) so agents can clearly distinguish email data from their own instructions.