Everybody talks about "owned audience" like a bank balance — you build it once, and it's yours forever. But the two owned channels most ecommerce and SaaS teams run don't hold value the same way. An email list quietly erodes at the edges: inbox placement slides, tabs swallow your sends, and a big slice of subscribers stop opening long before they ever unsubscribe. An SMS list decays too, but along a very different curve — and mostly through explicit opt-outs, not silent invisibility.
That difference — call it reach durability — is the thing that should nudge how you split budget between the two. Not the open-rate stat you've seen a hundred times.
Full disclosure: I work for Ready, an SMS platform. So I have a horse in this race. I'm going to show you the math anyway, including the parts where email is the smarter spend.
The two kinds of list decay
Every owned list loses reach over time. But the mechanism matters, because one kind is reversible and one mostly isn't.
Silent decay is when a subscriber is technically still on your list but never actually sees you. For email, that's landing in the Promotions tab, gradual spam-folder drift after low engagement, or a mailbox provider deprioritizing you because your open rates sagged. The contact is "on the list" but the reach is gone. You can't see it clearly in your dashboard — your list count looks fine.
Explicit decay is when someone leaves on purpose — an unsubscribe, a STOP. It's honest. It shows up in your numbers. And it's a cleaner signal, because the people who stay are the people who chose to.
Email leans heavily on silent decay. SMS leans almost entirely on explicit decay. That's the whole argument in one sentence, and the rest of this post is just putting numbers on it.
Where email quietly loses reach
Let's build a rough model. These are industry-approximation ranges, not lab-precise figures — treat them as directional.
Say you have 50,000 email subscribers and you send a promo. Here's the funnel that actually decides how many humans lay eyes on it:
| Stage | Approx. retention | Remaining reach |
|---|---|---|
| Subscribers on list | — | 50,000 |
| Land in inbox (not spam/blocked) | ~90% | 45,000 |
| Land in Primary vs Promotions tab | ~50–75% end up in Promotions | ~11,000–22,000 in Primary |
| Actually opened | ~20–35% of delivered | ~9,000–15,000 opens |
The Promotions-tab hit alone strips a big chunk of practical reach — plenty of buyers never open that tab on a weekday. Stack that on top of normal open-rate decay and you're often reaching a fraction of the list you paid to acquire. And engagement decays over months: a subscriber who joined 18 months ago and hasn't opened in 60 days is functionally dark, even though your ESP still bills you for them and counts them in your "audience size."
None of this is email being bad. Email is excellent — cheap, deep, great for long-form. It's that the deliverable, actually-seen reach of an email list is a lot smaller and stickier-downward than the raw subscriber count implies.
Where SMS loses reach (and where it doesn't)
SMS has almost no silent-decay layer. There's no Promotions tab. There's no "seen 40% of the time" — an opted-in, registered 10DLC message that clears carrier filtering lands in the one thread the phone shows by default, and open rates for opted-in lists commonly land in the 90%+ range because people read texts.
So what does eat SMS reach?
- Opt-outs (STOP). Real, explicit, and honest. Over-send and this number climbs fast — we've written before about how the 4th text in 7 days is where unsub rates double.
- Carrier filtering. This is the SMS equivalent of the spam folder, and it's the one to take seriously. Unregistered traffic, shady link shorteners, and use-case mismatches get quietly dropped. This is largely preventable — register properly, use a branded domain, keep your content clean.
- Number churn. People change numbers occasionally, but far less often than they abandon an email address.
The key structural difference: SMS's biggest reach-killer (filtering) is an infrastructure problem you can fix and keep fixed, whereas email's biggest reach-killer (tab placement and engagement-based deprioritization) is a moving target set by mailbox providers you don't control.
Putting durability side by side
Here's the same 50,000 contacts, modeled as deliverable reach that a human actually sees, freshly acquired vs. 18 months later.
| Email (50k) | SMS (50k) | |
|---|---|---|
| Practical seen-reach, fresh | ~9,000–15,000 opens | ~40,000–45,000 read |
| Practical seen-reach, ~18 mo later | often 30–50% lower (engagement decay + tab drift) | mostly intact minus opt-outs (~5–15% attrition) |
| Primary decay mechanism | silent | explicit |
| Fixable by you? | partly | mostly yes |
Read that top row again. The gap in seen reach per contact is why an SMS subscriber tends to be worth several times an email subscriber — a point we do the per-contact math on in SMS is worth 3–5x an email subscriber. Durability compounds that gap over time.
The catch: SMS costs money per send, email basically doesn't
This is where honesty earns its keep. Email's marginal cost per send is close to zero. SMS is not. On Ready, a single 160-character segment is $0.02 + $0.0045 carrier pass-through = $0.0245 all-in.
A one-segment blast to that 50,000 SMS list:
- 50,000 × $0.0245 = $1,225 per send
Add an emoji or run long and each message splits — a 175-character promo with an emoji becomes 3 unicode segments (unicode caps at 70 chars/segment):
- 50,000 × 3 × $0.0245 = $3,675 per send
Email to 50,000 might cost you a few dollars of ESP overage, if that. So SMS has to earn its per-send cost every single time. It usually can — because the seen-reach is 3–4x higher and response rates on opted-in lists often land around 30–50% — but the discipline required is real. You cannot batch-and-blast SMS the way you can email. Every extra send has a floor cost and an opt-out cost. That's exactly why there's a revenue-per-send peak past which a 5th monthly text loses money.
If you cross 50,000 segments in a calendar month, Ready drops you to the Growth rate ($0.016 + $0.0045 = $0.0205 all-in) automatically — no plan to pick, it just applies.
So where should owned-audience budget skew?
Not "all SMS." The durable-reach argument says something more specific:
- Use email for breadth and depth. Big catalog, storytelling, newsletters, long nurture — the stuff that's cheap to send and doesn't need to be read within the hour. Email's near-zero marginal cost makes it the right home for high-frequency, low-urgency reach.
- **Use SMS for the moments where being seen is the whole point.** Abandoned cart, back-in-stock, flash-sale windows, VIP drops, shipping and delivery updates. High intent, time-sensitive, worth $0.0245 to guarantee it's read.
- Protect SMS's durability like it's the asset it is. Register your 10DLC properly, honor STOP automatically, cap frequency, and don't torch the list on a Tuesday-nothing-promo. The reason SMS reach stays durable is that you didn't abuse the one thread the customer let you into.
- **Skew incremental budget toward SMS as your list matures.** A fresh email list performs well; an aging one silently loses reach you can't easily win back. SMS reach holds. Over a two-year horizon, the dollar you spend building and maintaining the SMS list keeps buying deliverable attention longer.
There are absolutely moments where SMS is the wrong call and sending anyway burns your opt-in — we laid those out in 5 ecommerce moments where SMS loses to email. Durability doesn't mean always text. It means the SMS reach you build tends to stay bought.
The practical takeaway
Your email list count and your SMS list count are not the same kind of number. Email erodes silently through tabs and engagement decay, so its seen reach is smaller than it looks and drifts downward over time in ways you can't fully control. SMS erodes explicitly through opt-outs and (fixable) carrier filtering, so its seen reach stays close to its list count as long as you register properly and don't over-send.
That durability is worth paying a per-segment cost for on the messages where being read now is the point. Run email for breadth, run SMS for the moments that convert, and defend the SMS list's health so it stays durable.
If you want to see what your send volumes would actually cost — and how the automatic Growth-tier drop kicks in past 50k segments — the Ready platform and pricing are here, and you can start with 2,500 free credits, no card to test the seen-reach difference on your own list before you commit a dollar.