Send & Retain vs Customer.io
Customer.io runs journeys across email, push, SMS, and in-app. Send & Retain does email only, run by your AI agent through an API.
✓Free to start. Unlimited contacts on every tier.
One system, end to end
Product event accepted
Trigger
Paused automation inspected
Run
Delivery state retained
Report
[ 01 / 05 ]The short answer
What's the difference between Send & Retain and Customer.io?
Customer.io is a customer engagement platform for journeys across several channels. Send & Retain is an email API plus a remote MCP server, focused on transactional and marketing email that your AI agent runs.
- Both trigger messages from product events and both send transactional email.
- Customer.io covers push, SMS, and in-app. Send & Retain covers email only.
- Customer.io pricing grows with profiles. Send & Retain is priced on sends, with unlimited contacts.
Context decides the send
Trial ending in 3 days
Audience
Plan is Pro
Condition
Renewal reminder
Message
Run recorded
Evidence
[ 02 / 05 ]Side by side
How do Send & Retain and Customer.io compare?
Channels
Email, push, SMS, in-app, and more
Email only
Journeys
Visual multichannel journeys with segments
Email automations triggered by product events, always created paused
Newsletters
Broadcasts to segments
No blasts. Every email goes to one person
Transactional email
A transactional API alongside journeys
Same API and contact record as your automations
Who does the work
A marketing team in the dashboard, or an agent over its MCP server
Your AI agent over MCP, with your approval, plus a dashboard
Sending
Customer.io's sending, or your own SMTP server or email provider
Our platform, or your own Resend or SendGrid key, with failover
Pricing
Grows with the number of profiles
Priced on sends. Unlimited contacts on every tier
[ 03 / 05 ]Which to pick
Which should you choose?
Pick by how many channels you really need.
- Choose Customer.io if push, SMS, or in-app messages are part of the same journeys as your email.
- Choose Customer.io if a marketing team builds and runs complex journeys in a visual canvas every day.
- Choose Send & Retain if email is the channel that matters and you want your AI agent to run it.
- Choose Send & Retain if your list is large and you'd rather pay for sends than for profiles.
[ 04 / 05 ]Moving over
How do I move from Customer.io to Send & Retain?
Move email journeys one at a time. There's no Customer.io connector, so your agent rebuilds them.
Pick an email-only journey
Start with one that doesn't depend on push, SMS, or in-app steps.
Import people and unsubscribes
Import unsubscribes as your block list first, then people as contacts.
Send your events here too
Send the same product events to the Send & Retain events API.
Rebuild, test, switch
Your agent rebuilds the journey as a paused automation. Test it in your inbox, then turn it on and stop the old one.
Built into every step
Questions people ask us
Move one email journey first.
Rebuild one journey as a paused automation, test it in your inbox, and switch it when it works.