Is Mailers.io an email provider?

No. Mailers.io is an orchestration and control layer that sits above email providers. Customers connect their own Amazon SES, Mailgun, SendGrid, Resend, Postmark, Brevo, Gmail / Google Workspace SMTP, Outlook / Microsoft 365 SMTP, or any SMTP server.

How does quota-aware routing work?

Mailers.io distributes sending across connected providers using per-provider hourly and daily caps and a priority order. When a provider approaches its cap or returns a transient error, the router automatically falls back to the next eligible provider with no code changes.

Which providers can I connect?

Amazon SES, Mailgun, SendGrid, Postmark, Resend, Brevo, Gmail / Google Workspace SMTP, Outlook / Microsoft 365 SMTP, and any RFC-compliant SMTP server. New providers are added over time.

Is there a free plan?

Yes. The Free plan is $0 forever and includes 2,500 credits per month, one connected provider, campaigns, API access, and community support. No credit card required.

Does Mailers.io support transactional and marketing emails?

Yes. Transactional sends go through the unified API. Marketing, lifecycle, and cold-email sends run via the campaigns and automations modules. Per-provider routing rules can segment reputation by use case.

How is compliance handled?

Compliance is built into the platform: global unsubscribe, List-Unsubscribe header, bounce and complaint suppression, do-not-contact lists, domain-level suppression, per-workspace suppression, and full audit logs. A signed DPA is available at https://mailers.io/dpa covering GDPR Article 28, SCCs Module 2, UK IDTA, Swiss FADP, and CCPA/CPRA service-provider terms.

Does Mailers.io include inbox or reply management?

No. Mailers.io does not sync replies or provide a unified inbox. Replies are delivered to whichever mailbox receives them on the connected provider.

Can I white-label Mailers.io?

Yes, on the Enterprise plan. White-label covers the dashboard, email surfaces (unsubscribe, preference center, tracking), and per-client sending domains.

Do I need to move my domains or DNS?

No. You keep your existing sending domains and DNS. Mailers.io verifies DKIM, SPF, and return-path alignment against your records and uses your provider accounts to send. Domains, reputation, and billing stay under your control.

Is this a reseller or proxy for email providers?

No. Mailers.io does not resell sending capacity and does not proxy your mail through our own infrastructure. We orchestrate your connected providers. You pay them directly. If you leave, your accounts are still yours.

What if a provider I use is not in the list?

Connect it over SMTP. Almost every provider exposes an SMTP interface that Mailers.io can drive with the same routing, caps, and analytics as an API-native driver. For high-priority providers without a driver yet, let us know — drivers ship often.

How does Mailers.io route across providers?

You configure per-provider hourly and daily caps, priority, and eligibility rules (by domain, purpose, or campaign). The router evaluates which providers are in-cap and eligible, then dispatches the send. When a provider nears its cap, traffic shifts to the next eligible one automatically.

Can I isolate providers per domain, tenant, or campaign?

Yes. Providers can be scoped by sending domain, by workspace (for agencies and SaaS multi-tenant setups), or by campaign purpose. This is how teams separate transactional, marketing, and cold outreach across different reputation pools.

Are analytics and webhooks unified across providers?

Yes. Delivery, bounce, complaint, open, and click events are normalized into a single schema regardless of provider. Webhooks, dashboards, and the analytics API all speak the same shape — no more provider-specific event mapping in your code.

Is there a limit on how many providers I can connect?

No hard limit on the number of connections. Plans differ on included connections and features, but the core ability to connect multiple providers is central to the product — not a gated add-on.

Integrations

Keep your sending stack. Wire it into one control plane.

Mailers.io is provider-agnostic. Connect the providers, SMTP servers, and mailbox accounts you already use, then operate every send from one dashboard, one API, and one set of routing rules.

Start Free See supported providers

API-native drivers: 9+
API-native drivers
RFC-compliant SMTP: Any
RFC-compliant SMTP
Gmail & Microsoft 365: OAuth
Gmail & Microsoft 365
You own the accounts: 100%
You own the accounts

Chapter 01 · Supported providers

Connect what you already run. No migration required.

API-native drivers for the major sending providers, OAuth for mailbox-based senders, and SMTP for everything else. You keep the accounts, the billing, and the deliverability history. Mailers.io adds the orchestration layer.

API + SMTP

Amazon SES

High-volume transactional + marketing sending at cloud-native cost.

Multi-region (us-east, eu-west, ap-*)

·API + SMTP endpoints
·Sub-account routing
·SNS event forwarding
·Configuration sets & IP pools

API

Mailgun

US and EU region support with per-domain sending and strong analytics.

US & EU regions

·Per-domain sending
·Tag-based analytics
·Webhook ingestion
·Bounce & complaint sync

API

SendGrid

Mature API with subusers, IP pools, and detailed event streams.

Global

·v3 REST API
·Subusers & IP pools
·Event webhook
·Click / open tracking

API

Resend

Modern developer API. Excellent for teams building React-first email.

·Modern REST API
·React Email-compatible
·Low-latency sending
·Event webhooks

API

Postmark

Transactional and broadcast streams with strong reputation discipline.

·Transactional streams
·Broadcast streams
·Bounce classification
·Event webhooks

API

Brevo / SparkPost / Mailjet

European-friendly providers with flexible sub-account models.

EU data residency options

·API-native drivers
·Sub-account routing
·Bounce + complaint sync
·Per-domain isolation

OAuth

Gmail / Google Workspace

OAuth-connected mailboxes for low-volume outbound.

·OAuth connection
·Per-mailbox daily caps
·No delegated access required
·Ideal for low-volume sends

OAuth

Microsoft 365 / Outlook

OAuth-connected tenants and mailboxes with audit-friendly controls.

·OAuth connection
·SMTP fallback
·Tenant-level controls
·Audit trail alignment

SMTP

Custom SMTP

Any RFC-compliant SMTP server — including your own relays.

·Any RFC-compliant SMTP host
·TLS + STARTTLS
·Custom auth profiles
·Internal Postfix / Exim / Halon

Missing a provider you depend on? Custom SMTP handles most edge cases. For native API drivers, new providers ship on a regular cadence — tell us what you need.

Chapter 02 · How connections work

Four steps, then sending is just sending.

Connecting a provider should not require a migration project. Mailers.io keeps the path short — authenticate, verify, route, monitor. No proprietary sending infrastructure in between.

01
Authenticate
Paste API credentials, run an OAuth flow, or add SMTP auth. Mailers.io never asks for more access than the provider gives you.
- ·API keys / tokens
- ·OAuth for Gmail & Microsoft 365
- ·SMTP username + password
02
Verify
Domains are verified with DKIM, SPF, and return-path records. Mailboxes confirm identity. Credentials are validated against a live send test.
- ·DKIM + SPF alignment
- ·Return-path checks
- ·Live credential handshake
03
Configure routing
Set hourly and daily caps, priority, and eligibility rules. Group providers by purpose — transactional, marketing, cold outreach — or by domain.
- ·Hourly / daily caps
- ·Priority weighting
- ·Domain & purpose rules
04
Send & monitor
Every message goes through the same API. Analytics, health checks, and audit logs are normalized across providers — no more cross-dashboard archaeology.
- ·Unified send API
- ·Health monitoring
- ·Per-provider analytics

Chapter 03 · Why multi-provider

One provider is a bet. A provider stack is infrastructure.

Serious outbound programs eventually hit provider ceilings — throttling, policy changes, reputation incidents, regional outages. A multi-provider setup is how mature teams stay operational without rewriting application code every time.

No single point of failure
If one provider throttles, goes down, or tightens policy, your traffic keeps moving. Routing rules shift send volume to eligible providers instead of dropping mail on the floor.
Right provider for the right job
Use SES for high-volume, Postmark for transactional reputation, Gmail for low-volume outreach. Mailers.io lets each provider do what it does best, under one policy.
You own the relationships
Accounts, contracts, domains, and reputation stay in your name. Mailers.io is a control layer — never a middleman reselling sending capacity back to you.
One view across the stack
Normalized analytics, audit logs, and health signals across every provider. Stop stitching together dashboards to answer basic deliverability questions.

Chapter 04 · Architecture

Where Mailers.io sits in your stack.

Mailers.io is the orchestration layer. Your application talks to one API. Mailers.io evaluates routing rules, selects an eligible provider, and dispatches the send. Events flow back through a normalized webhook stream.

Layer 01

Your application

Any service, worker, or dashboard that needs to send mail.

Layer 02 · Mailers.io

Orchestration

Unified API, quota-aware router, suppression, compliance, audit.

/v1/send
Router
Suppression
Webhooks

Layer 03

Your provider pool

Amazon SES
Mailgun
SendGrid
Resend · Postmark · Brevo
SMTP / Gmail / Outlook

Your code

One integration

Write against /v1/send once. Never branch on provider again.

Your accounts

Stay in your name

Domains, billing, reputation — all under your control, not ours.

Your data

Normalized events

Bounces, complaints, opens, deliveries — same shape, every provider.

Chapter 05 · SMTP escape hatch

If it speaks SMTP, Mailers.io can drive it.

API-native drivers cover the big providers, but real sending stacks always have edge cases — internal relays, regional ESPs, compliance-scoped MTAs. Custom SMTP connects any of them and still fits inside quota-aware routing, suppression, and unified analytics.

Any RFC-compliant SMTP host
TLS and STARTTLS
Custom authentication profiles
Internal relays — Postfix, Exim, Halon
Per-server caps and priority
Health checks with automatic standby

SMTP connection

relay-eu-1.internal.acme.com

healthy

Host: relay-eu-1.acme.com
Port · TLS: 587 · STARTTLS
Hourly cap: 12,000
Daily cap: 180,000
Priority: 2 — fallback
Purpose: transactional

Integrations FAQ

Straight answers about what connects and what doesn't

The honest version of the integrations conversation — before procurement asks the same questions.

API-native drivers for Amazon SES, Mailgun, SendGrid, Resend, Postmark, Brevo, SparkPost, Mailjet, and ElasticEmail. OAuth for Gmail / Google Workspace and Microsoft 365 / Outlook. SMTP for any RFC-compliant sending service or internal relay. New API drivers ship on a regular cadence.

Your stack · Our orchestration

Bring the providers. We'll handle the orchestration.

Connect your first provider in minutes. Keep the accounts, the domains, and the deliverability history. Gain the control plane your outbound program has been missing.

Start Free Explore the API

No credit card required
·
Bring your own providers
·
SMTP, API, and OAuth supported