A cold email API that respects how cold email actually works.
Send cold outbound at volume across multiple providers and domains, with per-domain suppression, quota-aware rotation, and audit trails deep enough for compliance reviews.
- Many providers
- 1 APIMany providers
- Suppression
- Per-domainSuppression
- Built in
- RotationBuilt in
- For every event
- WebhooksFor every event
One API for cold email, across every provider and domain.
Cold email operators rarely run on a single provider or a single domain. Rotation across sending domains, provider pools, and IP groupings is the difference between a campaign that works and one that burns reputation on day three.
Mailers.io exposes a single API that handles the rotation. Your application calls one endpoint; we decide which provider, which domain, and which sending server gets the message — based on quotas, priority, and health.
One call. Platform picks the right sending path.
- Step 1
POST the send
Send subject, body, from, to, list, and optional routing hints. The API is REST; SDKs handle auth and retries.
- Step 2
Platform routes
Suppression is checked. Quota-aware rotation chooses the sending server. Failover kicks in on provider errors.
- Step 3
Webhooks fire
Delivered, bounced, complained — every event reaches your webhook endpoint with provider attribution.
Cold-specific capabilities, not re-skinned transactional.
Provider rotation
Across providers, sending domains, and IP pools — with priority and quota limits you define.
Per-domain suppression
Unsubscribe and DNC scoped to a specific sending domain so cold lists stay isolated from transactional.
Quota-aware sends
Caps per hour and per day enforce at the platform level. Sends queue instead of failing when capped.
Domain + pool separation
Keep cold pools isolated from transactional pools so reputation issues stay contained.
Automatic failover
When a provider errors, pool members take over. No manual rotation scripts.
Full audit trail
Every send recorded with provider, server, domain, response, and timing for compliance review.
Event webhooks
Delivered, bounced, complained, and unsubscribed events push to your webhook(s) in real time.
Idempotent requests
Idempotency keys prevent duplicate sends on retry. Safe for distributed worker pools.
- You run cold email at volume across multiple providers
- You rotate sending domains and need suppression scoped per domain
- You want reputation isolation between cold, transactional, and marketing
- You want a single API your application can rely on long-term
- We do not guarantee inbox placement — deliverability depends on domain reputation, content, and provider behaviour
- Cold email must still comply with CAN-SPAM, GDPR, and each provider's AUP
- Reply handling and inbox UIs are not part of this platform
Questions answered clearly.
Ship cold email at volume. On your stack, your domains, your terms.
A single API that rotates across every provider and domain you attach — with suppression and audit trails that hold up under review.