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

Limit	Value
External recipient addressbook slots	5 per account
API rate limit (general)	100 requests/minute
API rate limit (auth endpoints)	20 requests/minute
Daily send quotas	Enforced per account
Hourly send quotas	Enforced 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:

Header	Description	Present on
X-RateLimit-Limit	Maximum requests per minute	All responses
Retry-After	Seconds until quota resets	429 responses only
X-RateLimit-Remaining	Requests 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.

Behavior	Detail
Auto-population	New external addresses added when you send email
Slot limit	5 external addresses per account
LRU eviction	Least recently used entry auto-replaced after 5 days of inactivity
Exempt addresses	@inboxapi.ai, @inboxapi.io, @inboxapi.dev — unlimited, never counted