SMS and email are not interchangeable channels — they sit at different points in the attention economy. SMS is a tap-on-the-shoulder medium that excels at time-sensitive, high-intent moments such as order confirmations, shipping updates, flash promotions, restock alerts, and appointment reminders. Email is a wider canvas built for storytelling: long-form nurtures, catalog merchandising, editorial content, receipts with line-item detail, and lifecycle education. Strong programs use both, routed by the consent the subscriber gave you and the expectation they have for each inbox.
The economics differ as well. SMS carries a per-segment cost (and a strict 160-character payload before it splits), so every send needs to justify itself against margin. Email's marginal cost is closer to zero, which makes it the natural home for nurture, content, and broad merchandising. As a starting heuristic, we point clients toward email for anything that needs more than two sentences, multiple links, or visual merchandising — and toward SMS for anything tied to a deadline, a queue position, or a transactional event the subscriber explicitly cares about. When in doubt, ask whether the message earns its way into someone's pocket on a Saturday night; if it does not, it is probably an email.
Cadence and creative length follow from the channel. On SMS we cap most marketing programs at four to eight messages per month with a clear "Reply STOP to opt out" footer, treat MMS as a deliberate creative upgrade rather than a default, and avoid back-to-back sends within the same 24-hour window. On email, weekly is a floor for engaged subscribers and three to four touches per week is a ceiling for sale events, with sunset rules that move dormant addresses out of the active program before they damage deliverability. The two channels also need shared suppression rules: a customer who just purchased should not receive the same promo on both inboxes, and a subscriber who has opted out of SMS should still see relevant email — and vice versa.
Consent posture is where many programs quietly break. SMS requires prior express written consent in the U.S. under the TCPA, and that consent does not automatically extend to email; nor does an email subscription extend to SMS. We build collection points so each channel has its own checkbox or keyword opt-in, its own disclosure language, and its own log of when, where, and how the subscriber consented. That separation makes it straightforward to run the channels at different cadences without creating a compliance gap, and it preserves the option to retire one channel without losing the other.
If you are deciding the budget split, start with three inputs: contribution margin per order, message complexity, and compliance posture. High-margin, low-complexity offers (a flash sale on a hero SKU) lean SMS; low-margin, high-complexity offers (a bundle with multiple comparison points) lean email. Then prove the split with a holdout — a randomized 10–20% of the audience that does not receive the SMS arm — and read incremental revenue rather than attributed clicks. That is the only way to know whether SMS is adding revenue or simply re-attributing what email would have closed anyway. Want a working version of this split for your program? Call (888) 338-9816 or email onboarding@gofluxmarketing.com.