How do Customer.io and Resend prices compare?

Customer.io: custom or unlisted usage pricing at 25,000 profiles. Resend: $90/month on Scale at 100,000 emails. Different billing units are not an equal-workload comparison. Estimates exclude unlisted add-ons and taxes.

What matters for transactional email?

Review SMTP or API integration, domain authentication, bounce and complaint events, suppression handling and delivery-log retention.

Can I compare marketing and agent email by sends?

Only when the published plan actually bills by sends. Contacts, subscribers and inboxes stay in their own billing units.

What features and free access does Customer.io list?

Behavioral messaging, Lifecycle workflows, Event triggers. Free access: Trial. Check plan-specific availability and current terms on the provider's official pricing page.

What features and free access does Resend list?

React Email, Simple API, Webhooks. Free access: 3,000 emails/mo. Check plan-specific availability and current terms on the provider's official pricing page.

Email APIs · side by side

Customer.io vs Resend

Compare Customer.io, Resend by sending volume, delivery webhooks, inbound email, domain limits and retention.

Email APIs pricing calculator

These providers bill in different units. Each estimate uses its own workload; there is no same-volume price winner.

Customer.io

Number of profiles

25K

Resend

Monthly emails

100K

Customer.io

Custom / not listed

Custom / unlisted usage pricing · 25K profiles

Resend

$90 / mo

Scale · 100K emails

Listed USD plan fees and tracked usage only. Unlisted compute, transfer, extras, taxes and contract terms are excluded. Custom or unsupported plan usage is not estimated.

Email APIs overview & pricing

Email APIs	Customer.io	Resend
Provider	Customer.io	Resend
Billing unit	profiles	emails
Plan at selected usage	Custom / unlisted usage pricing	Scale
Monthly estimate	Custom / not listed	$90/mo
Workload	25K profiles	100K emails
Free access	Trial	3,000 emails/mo
Published plans	Essentials, Premium, Enterprise	Free, Pro, Scale, Enterprise
Prices checked	2026-10-08	2026-10-08

Provider

Customer.io: Customer.io
Resend: Resend

Billing unit

Customer.io: profiles
Resend: emails

Plan at selected usage

Customer.io: Custom / unlisted usage pricing
Resend: Scale

Monthly estimate

Customer.io: Custom / not listed
Resend: $90/mo

Workload

Customer.io: 25K profiles
Resend: 100K emails

Free access

Customer.io: Trial
Resend: 3,000 emails/mo

Published plans

Customer.io: Essentials, Premium, Enterprise
Resend: Free, Pro, Scale, Enterprise

Prices checked

Customer.io: 2026-10-08
Resend: 2026-10-08

Email APIs monthly cost

Customer.io: Not pricedResend: $90

Different workloads, separate estimates

Separate transactional delivery from campaigns, outreach and agent inboxes. Compare monthly sends and daily caps; contacts, seats and inboxes are not sending allowances. Budget separately for dedicated IPs, validation and attachments.

Email APIs feature comparison

Email APIs	Customer.io	Resend
Single sign-on	Not listed	With add-on
Daily limit	Not listed	No limit
Inbound emails	Not listed
RESTful API	Not listed
SMTP relay	Not listed
Official SDKs	Not listed
Schedule emails	Not listed
Batch sending	Not listed
Open tracking	Not listed
Link tracking	Not listed
React Email	Not listed
Custom domains	Not listed	1,000
Additional domains	Not listed	With add-on
Dedicated IPs	Not listed	With add-on
Dedicated IP warming	Not listed
Pristine shared IPs	Not listed
Automatic suppression list	Not listed
Bounce details	Not listed
Multi-region	Not listed
Data retention	Not listed	30 days
Deliverability insights	Not listed
DKIM, SPF, DMARC authentication	Not listed
Webhook endpoints	Not listed	10 endpoints
Webhook events	Not listed	All events
Social login	Not listed
GDPR compliance	Not listed
SOC 2 Type II certification	Not listed
Penetration testing	Not listed
DDoS protection	Not listed
Automated backups	Not listed
Multi-factor authentication	Not listed
API key permissions	Not listed
Signed webhook endpoints	Not listed
Ticket support	Not listed
Slack support	Not listed
Urgent response SLA	Not listed
Deliverability expertise	Not listed
In-app documentation	Not listed
AI assistant	Not listed
AI credits / mo	Not listed	500

Single sign-on

Customer.io: Not listed
Resend: With add-on

Daily limit

Customer.io: Not listed
Resend: No limit

Inbound emails

Customer.io: Not listed
Resend

RESTful API

Customer.io: Not listed
Resend

SMTP relay

Customer.io: Not listed
Resend

Official SDKs

Customer.io: Not listed
Resend

Schedule emails

Customer.io: Not listed
Resend

Batch sending

Customer.io: Not listed
Resend

Open tracking

Customer.io: Not listed
Resend

Link tracking

Customer.io: Not listed
Resend

React Email

Customer.io: Not listed
Resend

Custom domains

Customer.io: Not listed
Resend: 1,000

Additional domains

Customer.io: Not listed
Resend: With add-on

Dedicated IPs

Customer.io: Not listed
Resend: With add-on

Dedicated IP warming

Customer.io: Not listed
Resend

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Which email providers fit your needs?

Customer.io features & plan notes

Behavioral messaging
Lifecycle workflows
Event triggers

Full pricing Official Pricing

Resend features & plan notes

React Email
Simple API
Webhooks
All Pro features
1,000 domains
Dedicated Slack channel
10 webhook endpoints
500 AI credits / mo
SSO with add-on
Dedicated IP with add-on

Full pricing Official Pricing

How to compare email providers

Browse Email APIs pricing

Customer.io vs Resend — FAQ

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