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

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Send limits

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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.

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Per-inbox cap

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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: 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.

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Rate limit responses

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

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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.