What email marketing plugin functionality (from any platform) maps to Klaviyo, Attentive, or Postscript on Shopify, and what's typically lost in translation?
Short answer
Email platform migrations carry contacts, unsubscribes and templates, not flows or segment logic, which are rebuilt in Klaviyo, Attentive or Postscript (Klaviyo Help Center, October 2026). Send history mostly stays behind: Klaviyo's Mailchimp sync brings only 90 days of opens and clicks, and only when that option is checked at setup (Klaviyo's Mailchimp guide, October 2026).
- Klaviyo built-in list sync
- Mailchimp, Campaign Monitor, Constant Contact, Mad MimiLists, unsubscribes and bounces sync through these integrations, except Mailchimp bounces on profiles already in Klaviyo; other platforms import by CSV file and upload suppressions by hand (October 2026).Source: Klaviyo Help Center (How to migrate from another email service provider to Klaviyo)
- Engagement history from Mailchimp
- 90 days of received, opened and clicked emailSynced once at setup if the 'Collect open and click data' option is checked, for campaigns sent in the last 90 days, A/B tests excluded; Mailchimp tags don't sync (October 2026).Source: Klaviyo Help Center (How to migrate from Mailchimp)
- Attentive opt-out imports
- Not in the self-serve uploaderAttentive's CSV uploader takes opt-ins only; opt-outs go through your Attentive contact or support, so suppression lists move by request (October 2026).Source: Attentive Help Center (Subscriber list uploads)
- Postscript email
- Live, onboarding brands from a waitlistPostscript onboards email brands in cohorts; its SMS plans run from a $49 monthly minimum spend to $500 a month, with Enterprise quoted (October 2026).Sources: Postscript (Postscript Email, Pricing)
Deploi’s call
An email program maps to Klaviyo, Attentive or Postscript as lists, unsubscribes and templates, while flows and segment logic are rebuilt. So rebuild the flows someone can tie to revenue and retire the rest. A migration is the only moment a team will honestly audit fifteen automations, and in our judgment many of them run on assumptions nobody has revisited since they were built.
BuyUse the destination's own import when
- The old platform is Mailchimp, Campaign Monitor, Constant Contact or Mad Mimi, whose lists, unsubscribes and bounces Klaviyo's integrations sync (Klaviyo Help Center, October 2026).
- The list sits under about 50,000 profiles with a handful of flows, which Deploi's Mailchimp to Klaviyo record scores BUY (Deploi Build vs. Buy, October 2026).
- Your segments run on Shopify purchase data, which Klaviyo syncs from Shopify itself, full order history included (Klaviyo Help Center, October 2026).
CustomizeScript the move around the import when
- The list holds 50,000 profiles or more, or SMS (text message) consent or complex flows are in play. The same Mailchimp to Klaviyo record scores that CUSTOMIZE, with Shopify as the source of truth for consent (Deploi Build vs. Buy, October 2026).
- Revenue rides on engagement segments and the old platform has no Klaviyo engagement-import guide (Klaviyo Help Center, October 2026).
- Attentive is the destination, because its self-serve uploader takes opt-ins only and opt-outs move through its team (Attentive Help Center, October 2026).
Basis: Mailchimp to Klaviyo on Shopify: Build or Buy the Migration?, our Build vs. Buy decision record, scored CUSTOMIZE.
What moves when you switch email platforms, and what doesn't?
Contacts, unsubscribes and templates move when you switch email platforms; flows, segment logic and most send history don't. Email is one layer of mapping a legacy platform's plugins onto Shopify, and Klaviyo's migration guides show where each asset lands (Klaviyo Help Center, October 2026).
| Asset | Moves? | How, per Klaviyo's migration guides |
|---|---|---|
| Contacts and lists | Yes | Built-in sync from Mailchimp, Campaign Monitor, Constant Contact and Mad Mimi; a CSV file otherwise |
| Unsubscribes and bounces | Yes | Synced by those integrations, except Mailchimp bounces on profiles already in Klaviyo; uploaded by hand otherwise |
| Email templates | With work | Through Klaviyo's custom template import |
| Autoresponders and flows | No | Rebuilt as Klaviyo flows, then turned live |
| Tags and segment logic | Tags by hand; segments no | Mailchimp tags are exported and imported manually; segments are re-authored |
| Send and open history | Partly | Mailchimp: 90 days of received, opened and clicked email if checked at setup; guides for five more platforms; profile properties elsewhere |
| Signup forms | No | Swapped for Klaviyo forms |
The middle rows set the schedule, because each one is authoring rather than import. In our judgment, fifteen live flows with branching and A/B splits take several weeks to build and test, and no comma-separated values (CSV) import shortens that.
Why do rebuilt segments come out wrong?
Rebuilt segments come out wrong because a segment is a query against a data model, and the old platform's model and Klaviyo's Shopify-native model hold different fields. So "purchased in the last 90 days and opened twice" can't be copied: it is re-expressed, then checked against a population you recognize. Compare counts before launch. If your top-customer segment held 4,200 people and the rebuilt one returns 6,800, the definition drifted.
Engagement segments start thin for the same reason. Klaviyo's Mailchimp sync brings 90 days of campaign opens and clicks when its open and click option is checked at setup, plus names, email addresses, ratings and locations, but no tags (Klaviyo's Mailchimp guide, October 2026). From a platform without a built-in integration, an opened-twice segment starts empty unless you upload engagement data as profile properties (Klaviyo Help Center, October 2026). Plan the first month's sends on purchase behavior instead, which arrives whole because Klaviyo syncs order history from Shopify itself and then updates in real time (Klaviyo Help Center, October 2026).
How do Klaviyo, Attentive and Postscript take in a legacy list?
Klaviyo syncs a legacy list and its suppressions from four email platforms. Attentive's uploader takes opt-ins only, and Postscript takes SMS (text message) lists as comma-separated values (CSV) files. So the destination decides how much of the move is manual. All three sell SMS and RCS (Rich Communication Services) messaging.
| Criterion | Klaviyo | Attentive | Postscript |
|---|---|---|---|
| Channels | Email, SMS, RCS, WhatsApp and push | SMS, email, push and RCS | SMS and RCS; email from a waitlist |
| List import | Built-in sync from four platforms, or a CSV file | CSV uploader for SMS and email lists | SMS by CSV upload; email migrated by Postscript's team |
| Opt-outs and suppressions | Synced, or uploaded to the suppression list | Uploader takes opt-ins only; opt-outs via Attentive's team | SMS uploads flag unsubscribed numbers in a status column |
| Entry price (USD) | Email $20 a month at 251 to 500 contacts; SMS from $15 | Free to install; pricing tailored | $49 monthly minimum, then $0.009 per SMS plus carrier fees |
Which destination fits which email and SMS program?
Klaviyo is the default destination for a $20M to $500M merchant consolidating email and SMS (text message) in one place, because segments built on Shopify order behavior work on day one. The Klaviyo, Omnisend and Attentive comparison makes the full platform case. Deploi's Klaviyo vs. Attentive record keeps Klaviyo for email-led programs and gives Attentive the brand where SMS is the headline channel with a dedicated owner (Deploi Build vs. Buy, October 2026). Attentive's listing adds in-house Telephone Consumer Protection Act (TCPA) experts and templates (Shopify App Store, October 2026).
Postscript suits an SMS-first brand that wants a specialist. Postscript Email exists, but Postscript onboards email brands in cohorts from a waitlist (Postscript, October 2026), so plan email elsewhere until your cohort opens.
The combination to avoid is two vendors capturing consent with no agreed source of truth for subscription status, where an opt-out recorded in one never reaches the other.
Does sender reputation survive the move to a new platform?
Sender reputation survives the move on your sending domain, not on the platform. Klaviyo says a domain's reputation carries over from the previous email service provider (ESP), and that "Deliverability issues will not automatically resolve by switching ESPs" (Klaviyo Help Center, October 2026). New infrastructure still has to warm, so send the first campaigns to your most engaged segment. Build that segment from whatever engagement history imported, or from purchase recency where none did. Run both platforms in parallel for two to four weeks, as Deploi's Mailchimp to Klaviyo record plans, so flows keep sending while the new platform warms (Deploi Build vs. Buy, October 2026). Keep each flow live on one platform at a time, pausing the old platform's copy once the new one is live (Klaviyo's Mailchimp guide, October 2026). How long Klaviyo's warming takes sets out each warming path.
When should you hold the email platform move?
Hold the email platform move when another change, a missing export or an unaudited program would make the results unreadable.
Deploi’s point of view
Our own position, from building on Shopify. Kept apart from the sourced facts above.
- What we’ve seen
- The engagement-history gap is the underestimated one. Teams plan for the flow rebuild and then discover their segmentation strategy depends on engagement data that came across thin or not at all.
- Where we disagree
- Vendor migration services are sold as full-service and are mostly contact and template work. The flow logic is yours either way, and outsourcing it hands your retention strategy to whoever is cheapest on the statement of work.
- What this page adds
- The asset-by-asset inventory of what transfers between email platforms as of October 2026, how much engagement history imports (90 days from Mailchimp), and how Attentive and Postscript take in a legacy list.
Decision records behind this answer
When this answer changes
- Klaviyo adds built-in sync or engagement imports for more email platforms, or changes the 90-day Mailchimp window.
- Klaviyo moves its App Store listing from SMS credits to per-message dollar pricing.
- Postscript opens email to every brand, ending the waitlist.
- Attentive's self-serve uploader starts accepting opt-outs.
- Klaviyo, Attentive or Postscript changes its entry prices or plan structure.
Related questions
This follows from How do we map a legacy platform's subscription-app integration to Recharge, Skio, or Loop Subscriptions, given the 2026 Recharge-Skio acquisition uncertainty?
- Klaviyo vs Omnisend vs Attentive: which is the right email-and-SMS stack for a $20M-$100M Shopify Plus brand?
Klaviyo wins email and segmentation for a $20M to $100M Shopify Plus brand; SMS (text messaging) is a separate decision.
- How long does a full Klaviyo migration off Mailchimp or ActiveCampaign realistically take for a $20M+ GMV Shopify Plus brand?
A Klaviyo migration for a $20M+ Shopify Plus brand runs on a month or more of sender warming, not build hours.
- How does a mid-market Shopify brand decide which Klaviyo flows to rebuild first after a full replatform, given limited implementation hours?
Klaviyo flow rebuilds after a replatform go in revenue order, so limited hours go first to abandoned cart, at $6.77 per email recipient on average (Klaviyo benchmark report, October 2026).
Sources
Every figure on this page traces to one of these. Official and vendor pages are checked on the date shown; Deploi records are our own published decisions.
- Klaviyo Help Center, How to migrate from another email service provider to Klaviyo
- Klaviyo Help Center, How to migrate from Mailchimp
- Klaviyo Help Center, How to warm your sending domain in Klaviyo
- Klaviyo Help Center, Shopify data reference
- Klaviyo Help Center, How to migrate your branded sending domain from a previous email service provider (ESP) to Klaviyo
- Klaviyo Help Center, FAQ 7/13 Mobile Messaging Update
- Klaviyo, Klaviyo: Email Marketing & SMS on the Shopify App Store
- Attentive, Attentive: AI-led Email & SMS on the Shopify App Store
- Attentive, Pricing
- Attentive Help Center, Subscriber list uploads
- Postscript, Postscript SMS Marketing on the Shopify App Store
- Postscript, Pricing
- Postscript, Postscript Email
- Postscript Help Center, Upload an Existing SMS Subscriber List
- Deploi Build vs. Buy, Mailchimp to Klaviyo on Shopify: Build or Buy the Migration?
- Deploi Build vs. Buy, Klaviyo vs. Attentive on Shopify: Which SMS Platform Wins?