Write-up · Marketplace app
6,200 to 24,800 SMS subscribers in six months, without burning the list
By Rhea Delgado, Principal SMS Strategist · Published July 26, 2026 · Figures illustrative and anonymized
A consumer marketplace app came to us with 6,200 SMS subscribers and a growth mandate: quadruple the list before the holiday quarter without the opt-out spiral that usually follows fast growth. Six months later the list stood at 24,800, campaign click-through held at 9.4%, and opt-outs averaged 0.41% per send. The whole story fits in one table.
| Metric | Before | After | Window |
|---|---|---|---|
| SMS subscribers | 6,200 | 24,800 | 6 months |
| Campaign CTR | 8.9% | 9.4% (held) | avg per send |
| Opt-out rate per send | 0.52% | 0.41% | avg per send |
| Delivery rate | 95.8% | 96.9% | monthly avg |
Where the growth came from
Three sources, in order of volume. Checkout opt-in did the heavy lifting because intent peaks at purchase; the consent language named the brand, disclosed message frequency, and stated that consent was not a purchase condition, exactly what 47 CFR 64.1200(f)(9) asks for. An exclusive-offer popup ran second, with the SMS offer set above the email offer. Keyword joins from in-app banners came third. EZ Texting's 2026 survey found 62% of consumers will opt in before a first purchase when the trade is clear; this program bore that out.
Why engagement held while volume quadrupled
Growth usually dilutes engagement because new subscribers get the same firehose as loyalists. We split the calendar instead: new joins entered a four-message welcome sequence, and blast campaigns went only to subscribers with a click or purchase in 90 days. The 9.4% CTR sits inside Klaviyo's published 8.9 to 14.5% “good” band, and the 0.41% opt-out average stayed inside Postscript's 0.33 to 0.88% percentile band the entire six months. Rhea's rule from six years of running marketplace SMS: list size is a vanity metric until the opt-out line stays flat for a quarter.
What carried over
Throughput planning mattered more than expected: the send volume quadrupled, so we re-vetted the 10DLC campaign early to keep the trust score's messages-per-second headroom ahead of Black Friday. That step is standard in our SMS compliance & deliverability service. The growth playbook itself, checkout opt-in first, is part of SMS program management. Sources: Klaviyo's campaign benchmark scales and Postscript's 2026 benchmark report.