Customer.io vs Mailchimp

What a "person" is in each tool

Customer.io's Add people guide breaks a person into identifiers, attributes, the events they perform, their relationships to objects (a company they work for, a class they take) and, for push, their devices. All five parts can group people into segments, start automations and personalise messages. Because objects are first-class, a B2B account can be modelled as an object with its own attributes, and an Object updated trigger can message everyone related to it, as the triggers page explains.

Mailchimp's unit is a contact in an audience. The tags, groups and segments layer on top of that, and imported columns map to audience fields. There is no company object on the pages we read, so account-level logic means putting the company in a field or tag and segmenting on it.

For a B2B SaaS this is the quiet divider. If your messages depend on which account a person belongs to, how many seats that account has activated, or whether an admin has done something, Customer.io's object model is built for it. If your messages depend on the person alone (a trial user, a webinar attendee, a newsletter subscriber), Mailchimp's contact model is enough.

Events: open to everyone, but the plan decides what they can do

Mailchimp's events article says the Events API endpoint is available to all users for event-based segments and event property merge tags, while paid marketing plans get the Event API trigger for automation flows. Contacts must already exist in the audience before you send them events. Accounts on Standard or higher can build multi-step flows from an Event API trigger; Essentials accounts can use the same trigger with a single-step flow, and Free has no event-based automation.

The same article sets the retention window for segmenting: custom event data can be used for 30 days after the event on Free and Essentials, 3 months on Standard and 18 months on Premium. A SaaS that wants a segment like 'created a report in the last 60 days' needs Standard to see that far back.

Customer.io's custom events guide describes events as part of the person: the call takes an event name and nested properties, may arrive before the person is identified, and then resolves to them. The plan table we read gates integrations and workspaces rather than event features, so an event-triggered workflow is available from the entry plan.

• On Mailchimp Essentials you can build a one-step flow from an event; a welcome-then-reminder sequence needs Standard.
• Mailchimp's event property segmentation shows as Premium in the plan table, even though the article's prose mentions Standard; check the current table before you buy.
• Customer.io events and people sent to a test or sandbox workspace still count toward the profile total on your bill.

Flow limits that change the design

The Mailchimp automation flows article sets concrete ceilings. A flow on Essentials can hold up to 4 steps; Standard and above allow up to 200. Standard also unlocks up to 3 triggers per flow, each with up to 5 filters, and an if/else split on up to 5 conditions. A flow can hold up to 10 wait-for-trigger rules.

A realistic B2B onboarding journey has a welcome email, a wait, a branch on whether the user connected a data source, a nudge for those who did not, a second branch on whether they invited a teammate, and an exit when they upgrade. Count the blocks and it passes 4 quickly. That is why the real Mailchimp price for event-driven onboarding is Standard, not Essentials.

Customer.io's triggers page documents entry conditions, exit conditions and frequency settings, and describes the workflow builder as the same on all plans. We found no step cap on the pages we read, but run your most complex journey through a trial before assuming none exists.

System email, SMS and CRM links

Customer.io's transactional guide says it does not charge extra to send transactional messages and keeps a separate IP pool with stricter thresholds for them. A domain in that pool can no longer send automations or broadcasts, so you need a dedicated subdomain. It also covers push, SMS and WhatsApp transactional messages through the same API.

Mailchimp promotes a transactional email and SMS API on a separate page, where templates from Mailchimp can be imported. That page lists no transactional price. Treat it as a second purchase and ask for a quote at your monthly volume.

On SMS, Customer.io's billing page says you are billed for SMS either through Customer.io or through your own Twilio account. Mailchimp lists SMS marketing as a feature of its plans. For a CRM link, Mailchimp's integration list includes Salesforce, while Customer.io places Salesforce and HubSpot (source and destination) among the Premium and Enterprise integrations.

Cost at 5,000, 10,000 and 25,000 contacts over two years

All figures are list prices in USD from Customer.io and Mailchimp, read on 2026-10-07, billed monthly.

At about 5,000 contacts, both list at $100 a month. Customer.io costs $1,200 a year and $2,400 over two years. Mailchimp's offer takes the first year to $600 ($50 x 12), so two years cost $600 + $1,200 = $1,800. If your company qualifies for Customer.io's Startup Program, year one is free and two years cost $1,200, which is $600 below Mailchimp.

At about 10,000 contacts, Customer.io is $145 ($1,740 a year, $3,480 over two years) and Mailchimp is $135 at list. With the 50% offer Mailchimp's first year is $810 ($67.50 x 12), then $1,620, so two years cost $2,430. Mailchimp is $1,050 cheaper over two years ($3,480 - $2,430). With Customer.io's free first year the order reverses: its two years cost $1,740 against Mailchimp's $2,430, so Customer.io is $690 cheaper.

At about 25,000 contacts, Mailchimp is $310 at list, $155 in the offer year. That is $1,860 + $3,720 = $5,580 over two years. Customer.io bills between $235 (20,000 profiles) and $325 (30,000) a month, so $5,640 to $7,800 over two years. From year three, Customer.io ($2,820 to $3,900 a year) is at or below Mailchimp's $3,720.

One more variable is send volume. Mailchimp Standard at 10,000 contacts allows 12 x 10,000 = 120,000 emails a month, and exceeding the contact or send limit triggers additional charges. Customer.io Essentials lists 1 million emails and charges $0.12 per 1,000 beyond that. A product that sends 20 lifecycle emails per user per month at 10,000 users sends 200,000, which is 80,000 over Mailchimp's allowance and well inside Customer.io's.

• Mailchimp's first-year discount applies to Standard bands; confirm your eligibility before you rely on it.
• Customer.io's selector shows stops (5,000, 10,000, 20,000, 30,000, 40,000, 50,000+), so intermediate counts need a quote.
• The Customer.io overage rate is $0.009 per extra profile: 600 profiles over the allotment add 600 x $0.009 = $5.40.

What the cheapest plans do not do

• Mailchimp Free: no event-based automation flows, 250 contacts, 500 sends a month; event data is usable for segments for 30 days.
• Mailchimp Essentials: 3 seats, flows capped at 4 steps, a single-step event flow, custom-coded templates that can be created but not sent, and event segments limited to 30 days of history.
• Customer.io Essentials: two workspaces, two object types, no managed deliverability, and a new account starts with a 500-email daily limit that rises to 10,000 a day after about two weeks.
• Customer.io Essentials leaves out the HubSpot and Salesforce connectors, the geofence trigger and warehouse export, which are Premium or Enterprise features.

Moving from Mailchimp to Customer.io

1. Export from Mailchimp's Audience page. Per the export guide, the download can be a ZIP with separate CSVs for subscribed, unsubscribed, non-subscribed and cleaned contacts; only Owners and Admins can export audiences, and files stay available for 30 days.
2. Map tags and groups to attributes or segments. Decide which become a profile attribute (plan, role) and which become an object relationship (the company).
3. Upload the subscribed file as a CSV of people, then handle unsubscribed people as suppressed so they are not re-mailed. Customer.io's docs note a CSV upload is a point-in-time snapshot, so set up real-time identification from your backend for anything live.
4. Send your product events through the data-in API so workflows start from real behaviour, and add a test person before you send to the audience.
5. Rebuild each Mailchimp flow as a workflow; use the extra headroom to add branches that Essentials' 4-step limit prevented.
6. Move system email onto the transactional API and warm up the sending domain gradually, because new Essentials accounts begin at 500 emails a day.

Moving from Customer.io to Mailchimp

1. Choose the plan first. If any flow runs from product events and has more than four steps, price Standard; Essentials allows only a single-step event flow.
2. Export people and attributes from Customer.io and list every event your workflows use. Event history stays behind, and Mailchimp can segment on events for only 30 days on Essentials or 3 months on Standard.
3. Run the Mailchimp importer once per marketing status. Unmatched columns are not imported, blank cells overwrite stored values on an update import, and a total above your plan's contact limit leads to extra charges.
4. Add the contacts before sending any events, since the Events API needs the contact to be in the audience first. Then send events from your backend and set the Event API trigger on each flow.
5. Represent companies with a field or tag, because there is no company object on the pages we read.
6. Replace Customer.io's transactional sends with Mailchimp's transactional API or another sender, and re-create domain authentication before you cut over.