Rate Limits

OpenMail enforces per-inbox send limits and cold-outreach throttling to protect deliverability. Learn how limits work and how to stay within them.

OpenMail enforces rate limits to protect domain reputation and ensure deliverability for all customers.

Send limits

Limit	Value	Scope
Burst	10/minute	Per inbox
Daily	200/day	Per inbox
Inbox creation	100/day	Per account

Cold outreach throttle

A “cold” send is an email to a recipient who has never sent an inbound message to this inbox. Cold sends have two independent caps, both reset per UTC day. A send only goes through if it is under both.

Per-inbox cap

Inbox age	Cold send limit
First 30 days	20/day per inbox
After 30 days	Standard daily limit (200/day)

Per-account cap

A separate cap applies across all of your inboxes combined, so adding more inboxes does not multiply your cold quota. It scales with your plan and loosens once your account is more than 30 days old:

Plan	First 30 days	After 30 days
Free	30/day	100/day
Developer	150/day	500/day
Launch	500/day	2,000/day

Enterprise plans are exempt from the per-account cap. These limits protect your domain reputation while it warms up. Relationship email (replies to recipients who have emailed you) is always “warm” and bypasses both caps.

Rate limit responses

When rate limited, the API returns 429 with a Retry-After header:

{
  "error": "rate_limit_exceeded",
  "message": "Max 10 sends per minute per inbox"
}

Why this matters

Fresh domains on shared IP pools need time to build reputation. If your agents send too much cold outreach too quickly, emails will land in spam - which hurts your agents’ effectiveness and your domain’s reputation. These limits exist to protect deliverability.

Contact us if you need higher limits or a dedicated sending IP.

For a complete warm-up strategy and content best practices, see Email deliverability.