Klaviyo vs Postscript: Cost, Fit and Switching SMS

Most pages ranking for “klaviyo vs postscript” run the same comparison-page shape as any two-tool matchup — a feature table, a verdict — and that shape hides the actual answer: Klaviyo and Postscript are not two competing answers to the same question. Klaviyo is an email-and-SMS platform. Postscript sends SMS only. A brand searching this phrase is usually deciding whether to run Postscript alongside Klaviyo, not instead of it, and no vendor page frames the comparison that way because both benefit from the search implying a straight swap.

What Do Klaviyo and Postscript Each Actually Do?

Klaviyo is an ecommerce-native email platform with SMS built in as a second channel on the same customer profile; Postscript is an SMS-only platform with no email product at all. That single fact decides most of what follows: a brand cannot replace Klaviyo with Postscript, because Postscript has nothing to say about the email side of a lifecycle programme. It can replace Klaviyo’s SMS channel specifically, running SMS on Postscript while email stays wherever it already is.

Klaviyo bills its Email and Email+SMS plans against active profile count, with SMS and MMS sending metered separately as message credits on top of that profile-based tier — the free plan includes $5 of mobile message credit a month, according to Klaviyo’s own pricing page. Postscript bills on a different mechanic entirely: a monthly base fee per tier (Starter at $0 with a $49 minimum spend, Growth at $100, Professional at $500, Enterprise custom) plus a per-message SMS rate that falls from $0.009 down to $0.007 as the tier rises, with a separate carrier fee — a blended US average of $0.00418 per SMS, per Postscript’s own carrier-fee documentation — added on top of every message on every tier. Neither vendor publishes a rate card that converts cleanly into the other’s terms, which is why a side-by-side dollar comparison needs your own SMS send volume as an input, not either pricing page alone.

Klaviyo vs Postscript, Compared

Read this table as a scoping exercise, not a scorecard: the row that actually decides the search is “replaces the other entirely,” and the answer is no in both directions. The real decision most brands searching this phrase are making is whether their SMS program has outgrown Klaviyo’s built-in channel enough to justify a dedicated platform and a second monthly bill.

What Does Moving an SMS List From Klaviyo to Postscript Actually Take?

It takes a subscriber-list export from Klaviyo and a compliance review by Postscript, not a data migration in the sense a full ESP switch would require — Postscript’s own migration guide states a 1-3 business day review once the list is submitted. The guide walks through a specific export: create a segment in Klaviyo filtered to profiles that “can receive sms marketing,” then export five fields for each contact — phone number, SMS marketing consent, the consent timestamp, the consent method, and the consent method detail. That CSV is uploaded through Postscript’s subscriber list upload form, and Postscript’s compliance team reviews it before the numbers go live in the account, requesting proof of the export criteria used where needed.

What that process does and does not cover is the part no comparison page states plainly:

• Transfers: the active subscriber list — phone numbers plus their consent status, timestamp and capture method. This is what “migrating” means in Postscript’s own documentation, and it is narrower than a full platform migration.
• Does not transfer automatically: a dedicated short code or a toll-free number, each of which Postscript documents as its own separate transfer process running on carrier timelines rather than the 1-3 business day list review. Opt-in keyword campaigns are not carried over either — they are reconfigured, and re-registered where a new number is involved.
• Does not exist to transfer: flow logic and automation triggers, because Klaviyo’s SMS flows and Postscript’s flows are built on two different platforms’ automation engines. Moving SMS platforms means rebuilding the win-back, abandoned-cart and post-purchase SMS sequences inside Postscript’s own flow builder — the same rebuild-by-hand problem that applies to a full ESP switch, scoped down to whatever SMS automations already exist.

Moving an SMS list from Klaviyo to Postscript is a materially smaller undertaking than switching ESPs, and it is worth naming the difference precisely: nobody migrates “off Klaviyo” to run Postscript, because Klaviyo’s email side keeps running. What moves is the SMS channel, and the review-and-upload process Postscript documents is closer to onboarding a new subscriber list than to a platform cutover. Where the effort actually lands is the flow rebuild — however many SMS-specific automations exist have to be recreated by hand inside Postscript’s builder, sized by flow count rather than list size, the same way any automation logic has to be rebuilt across any two marketing platforms that do not share a data model.

Both transfers also carry a compliance layer neither vendor puts on the pricing page. US carriers have blocked unregistered 10DLC (10-digit long code) traffic since February 2025, and every business sending SMS is verified once, at the brand level, through the Campaign Registry (TCR) — a carrier-mandated industry requirement, not a Klaviyo or Postscript-specific one. That brand-level registration does not automatically extend to a new number or short code provisioned on a different sending platform, which is exactly why Postscript’s compliance team reviews every uploaded list before activating it, and why the short code and toll-free number transfer guides Postscript documents separately run on carrier approval timelines rather than the platform’s own 1-3 business day review for a plain subscriber list.

How Do You Attribute Revenue When Email and SMS Run on Two Different Platforms?

Neither platform’s own reporting answers this once SMS moves to a separate system — Klaviyo shows combined email+SMS attribution only when both channels run inside Klaviyo, and Postscript reports SMS-attributed revenue on its own, with no view into what the same customer’s email touches contributed. The combined figure has to be built outside either platform, and there is a reliable way to do it without a data warehouse.

Both platforms attribute revenue through a last-touch or multi-touch model tied to a tracked link a customer clicked before ordering, and both write that attribution back to Shopify as order-level data — Klaviyo through its own tracked links and UTM parameters, Postscript the same way through its own link shortener. The method: tag every Klaviyo flow and campaign link with a consistent UTM source (utm_source=klaviyo) and every Postscript flow and campaign link with its own (utm_source=postscript), then pull Shopify’s own order attribution report filtered by those two UTM sources over the same date range. That gives a combined, channel-split revenue figure sitting in Shopify itself rather than trusting either platform’s self-reported number, which counts only its own sends and has no visibility into what the other channel touched on the same customer’s path to purchase.

The one input this method cannot supply on its own is a combined attribution model that weights overlapping touches — a customer who opened an email and clicked an SMS link on the same order shows up once in each platform’s own report, and a simple UTM pull double-counts that order across the two channel totals unless the export is de-duplicated on order ID before the totals are summed. The actual share of orders where both channels touched the same purchase is — metric to confirm; it is not something either platform surfaces, and confirming it requires pulling both UTM-tagged order sets and checking for shared order IDs directly, which is Shopify-side reconciliation work rather than anything either ESP or SMS platform reports natively.

What Do Deliverability, Opt-Out and Reply Rates Actually Look Like on Each?

Neither Klaviyo nor Postscript publishes a comparative deliverability, opt-out or reply-rate benchmark against the other, and no independent third party currently measures the two platforms against each other on those figures either — every comparison table ranking for this query lists features, never measured send performance. That gap is real and worth naming rather than filling with a plausible-sounding range: a reply rate depends on message content, send cadence and list quality at least as much as on the sending platform, so a bare platform-level number would be misleading even if one existed.

What is checkable, because both platforms document it themselves, is the mechanism each one runs to protect deliverability. Postscript’s carrier-fee documentation ties its message cost directly to carrier-level routing (Verizon, AT&T, T-Mobile, US Cellular each price differently), which is the same infrastructure that governs how reliably a message reaches a handset — a platform paying and routing through the same carrier relationships for every client is standardising on one set of carrier trust signals. Klaviyo’s SMS sends through its own registered short codes and toll-free numbers, carrying whatever sending reputation that specific number has built. Neither mechanism is inherently better; a newly provisioned number or short code on either platform starts with no history, which is why a migrated list — on either platform — is standard practice to warm up with smaller, higher-engagement sends before resuming full volume, rather than an assumption that platform choice alone determines deliverability.

Who Is Each Actually For — and Not For?

Klaviyo suits a brand that wants one platform covering both channels on one customer profile, with SMS as a supporting channel to a primarily email-driven programme. It is not a strong fit for a brand where SMS has grown into a primary revenue channel in its own right — Klaviyo’s SMS tooling is a channel inside a larger email product, not a purpose-built SMS platform with the keyword and compliance depth a heavy SMS programme needs.

Postscript suits a brand whose SMS list and cadence have outgrown a bolted-on channel and where SMS deserves dedicated tooling — dedicated short codes, granular keyword campaigns, a compliance team reviewing list imports. It is not a Klaviyo alternative for the email side of the business at all; adopting Postscript solves nothing for email, and a brand evaluating “Postscript instead of Klaviyo” has usually misread what Postscript is for.

Neither is the wrong choice for a scaling brand in isolation — the wrong choice is treating this as an either-or decision when the two products do not compete on the same channel.

When Does Running Both Actually Pay Off?

It pays off once SMS volume and revenue justify a second monthly bill and the operational overhead of running two platforms’ automations in parallel — broadly, once SMS has moved from an occasional campaign channel to a programme with its own flows, its own cadence rules and its own opt-out risk to manage actively. Below that point, Klaviyo’s built-in SMS channel is one less system to maintain, one shared customer profile instead of two, and no second compliance review to wait on for every list change. Sizing that threshold starts with knowing what the existing flow programme already earns rather than guessing at it — the flow revenue calculator puts a figure on current flow-driven revenue, which is the baseline a second platform’s cost has to be weighed against before adding it.

Above it, the case for a dedicated SMS platform is less about price and more about depth: Postscript’s carrier fee documentation, keyword tooling and dedicated-number infrastructure exist because SMS at real volume has compliance and deliverability demands an email-first platform’s bolted-on channel was not built to carry. Klaviyo’s own benchmark data puts automated flows at 41% of email revenue across more than 183,000 brands (vendor-reported) — a figure that only covers the email side, and a reminder that whatever platform sends SMS, the flows running on it need the same rigour the email flows already get, not a second-class version of the same automation.

Getting that rigour right across two systems — consistent UTM tagging so revenue attribution actually reconciles, flow logic rebuilt correctly rather than approximated, and a warm-up plan for a newly migrated number — is systems work spanning both platforms rather than a platform choice made once and left alone. That is what a lifecycle flows engagement is built to run, whether SMS stays inside Klaviyo, moves to Postscript, or the two run side by side.