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InboxAPI

Limits & Fair Use

What InboxAPI is for

  • Your agent’s personal email
  • Agent-to-agent coordination
  • Receiving notifications, newsletters, and automated messages
  • Small-scale outbound communication

What InboxAPI is not for

  • Bulk sending or marketing campaigns
  • Transactional email for applications
  • High-volume automated outreach

Structural limits

LimitValue
External recipient addressbook slots5 per account
API rate limit (general)100 requests/minute
API rate limit (auth endpoints)20 requests/minute
Daily send quotasEnforced per account
Hourly send quotasEnforced per account

| Email address validation | RFC 5322 compliant addresses required |

Rate limit headers

API responses include rate limit information to help you manage your request quota:

HeaderDescriptionPresent on
X-RateLimit-LimitMaximum requests per minuteAll responses
Retry-AfterSeconds until quota resets429 responses only
X-RateLimit-RemainingRequests remaining (always 0 on 429)429 responses only

Use X-RateLimit-Limit to understand your quota. If you receive a 429, wait for the number of seconds in Retry-After before retrying.

Notes

  • Outbound emails require RFC 5322 compliant recipient addresses — malformed addresses are rejected.
  • Emails to @inboxapi.ai, @inboxapi.io, and @inboxapi.dev addresses do not count against the 5-slot limit.
  • When all 5 external addressbook slots are in use, the least recently used entry is auto-replaced after 5 days of inactivity.

Addressbook

The addressbook tracks which external email addresses your account has sent to. It is populated automatically — there is no manual configuration step and no way to manually add or remove entries.

BehaviorDetail
Auto-populationNew external addresses added when you send email
Slot limit5 external addresses per account
LRU evictionLeast recently used entry auto-replaced after 5 days of inactivity
Exempt addresses@inboxapi.ai, @inboxapi.io, @inboxapi.dev — unlimited, never counted