If you run an ecommerce brand, you probably treat your email list and your SMS list as two columns in the same spreadsheet. Same contacts, same consent, same lifecycle. Mail them when you have something to say, suppress the bounces, move on.
That instinct is fine for email. It quietly creates risk on SMS, because the two channels decay differently, and they decay for different reasons.
An email address that's gone silent for 18 months is a low-yield asset. Worst case, it's a spam-trap or a dead inbox, you get a soft bounce, and your sender reputation takes a small ding. An SMS number that's gone silent for 18 months is something else entirely: it may have been recycled to a new human, your consent record has gone stale under carrier and TCPA expectations, and every text you send into that cohort raises your complaint rate, which is the exact metric carriers use to throttle everything you send, including the texts to healthy subscribers.
Full disclosure: I work for Ready, an SMS platform. So I have a reason to care whether your list stays clean. But the asymmetry below is real regardless of who you send with.
Why email consent ages gracefully and SMS consent doesn't
Email and SMS consent are governed by different machinery, and that's the root of it.
Email, in the U.S., runs under CAN-SPAM. CAN-SPAM is mostly a content and unsubscribe law, you need a working opt-out, an accurate sender, a physical address. It does not require prior express consent to email someone, and it doesn't put a clock on how fresh that consent has to be. So an old address is legally the same as a new one. The only thing that degrades is deliverability, and that degrades gradually.
SMS runs under the TCPA plus the carrier A2P 10DLC rulebook. The TCPA requires prior express written consent for marketing texts, and courts and carriers increasingly treat that consent as something with a freshness expectation, not a hard statutory number, but a practical one. The CTIA messaging principles lean on the idea that consent should reflect a current relationship. If someone opted in two years ago and you've sent nothing since, a plaintiff's attorney will argue that consent is stale, and the carrier's complaint-rate math doesn't care about your intentions at all.
Then there's number recycling. Mobile numbers get disconnected and reassigned constantly, the FCC's reassigned-numbers database exists precisely because this happens at scale. The person who opted in 18 months ago may not own that number anymore. Email addresses don't get reassigned to strangers. Numbers do.
The two failure modes, side by side
| Silent email address | Silent SMS number | |
|---|---|---|
| Governing rule | CAN-SPAM (content/opt-out) | TCPA + 10DLC (prior express consent) |
| Does consent "expire"? | No clock | Practical freshness expectation |
| Number/address recycled? | Essentially never | Routinely reassigned |
| Cost of mailing a dead one | Soft bounce, minor reputation ding | Complaint, possible TCPA claim, carrier throttling |
| Blast-level consequence | That one address underperforms | Complaint rate rises → all your sends get filtered |
The last row is the one operators miss. On email, a bad address hurts that address. On SMS, a pocket of stale numbers raising your complaint rate drags down delivery for the subscribers who do want to hear from you. We've written more about why the owned-audience durability math favors SMS when the list is healthy: SMS vs. email reach durability, but that durability advantage only holds if you keep the list fresh.
What "stale" actually looks like in practice
There's no bright-line "consent dies at X months." But here are the practical thresholds I'd watch, framed as approximations rather than legal advice:
- 0 to 6 months since last engagement or opt-in: fresh. Send normally.
- 6 to 12 months of silence: aging. Fine to keep mailing, but this is the window to re-engage before it gets risky.
- 12+ months of total silence, no clicks, no replies, no purchases: treat as a re-permission candidate, not a send target.
- 18+ months silent: stop blasting it. Re-permission or suppress.
Compare that to email, where an 18-month-silent address is just a candidate for a sunset flow, low stakes, you lose nothing by trying once more.
Why the cost math pushes you to prune, not keep
Operators hoard SMS subscribers because they feel expensive to acquire. They are. But look at what a stale cohort costs you to keep texting.
Say you have 40,000 SMS subscribers and 8,000 of them (20%) have been silent 18+ months. A standard 160-character promo is one segment. On Ready's Standard tier that's $0.02 + the $0.0045 carrier pass-through = $0.0245 per message.
Texting those 8,000 dead numbers on a single blast: 8,000 × $0.0245 = $196. Do that across 30 campaigns a year and you've spent ~$5,880 mailing people who, at best, ignore you and, at worst, file a complaint. And the complaint rate they generate is suppressing delivery to your other 32,000.
Now the downside math. TCPA statutory damages run $500 to $1,500 per text. One silent-number cohort that includes a reassigned number belonging to a known litigator, and a single blast is a four-to-five-figure exposure. We've laid this out before, scrubbing 100,000 contacts costs $500; one complaint costs $500 to $1,500 per text. The asymmetry isn't subtle.
How to run a re-permission pass
Re-permission is one last message to the aging cohort asking them to confirm they still want texts. Done right, it's cheap, it's defensible, and it cleans your complaint rate going forward.
1. Segment the cohort. Pull everyone with 12+ months of zero SMS engagement, no replies, no clicks, no purchases attributed to a text. Don't re-permission your whole list; you'll suppress people who are perfectly happy.
2. Scrub before you send. Before the re-permission blast, run that cohort through a litigator/DNC scrub. Ready's standalone scrub is $0.005 per contact, 8,000 numbers is $40, and it suppresses known TCPA-litigator and DNC-complainer numbers before they ever receive your message. This is the single highest-ROI $40 you'll spend on a stale list, because stale lists are exactly where recycled and litigator numbers hide. A list you scrubbed months ago is dirty again now; see how fast each list source rots.
3. Send one clear, honest message. Something like:
Still want deals from [Brand]? Reply YES to stay subscribed. We'll stop texting this number otherwise. Reply STOP to opt out. Msg&data rates may apply.
4. Honor the silence. Anyone who doesn't reply YES comes off the active send list. That's the entire point, you're trading reach you weren't really getting for a cleaner complaint rate and a defensible consent trail.
5. Keep the proof. Record the opt-in confirmation. If you ever switch platforms, those fields are what prove consent survived the move, don't let a migration silently reset it: the export fields that prove opt-in survived.
Where the platform does the boring parts for you
Re-permission only works if the opt-outs it generates actually stick. A few things worth having handled automatically:
- Automatic STOP/opt-out propagation. When someone replies STOP to the re-permission text, Ready honors it and propagates the opt-out so that contact can't be messaged again across your campaigns, not just the one that sent it. STOP also isn't the only word carriers treat as an opt-out; the full keyword set DIY setups miss matters here.
- Quiet-hours enforcement. A re-permission blast to an aged cohort is the worst possible time to text someone at 6am their time. Ready holds sends outside permitted local hours based on the recipient's area, which also reduces TCPA exposure.
- Consent/attestation capture. The YES replies and opt-in records build the audit trail you'll want if anyone ever questions the consent.
None of this makes you lawsuit-proof, compliance is ultimately the sender's responsibility. It just removes the manual steps where mistakes happen.
The takeaway
Email consent effectively doesn't expire; email just gets lower-yield as addresses go cold, and the worst case is a bounce. SMS consent carries a practical freshness expectation, the underlying numbers get recycled to strangers, and a cohort of silent subscribers actively drags down delivery and raises TCPA exposure for your whole list.
So treat the two lists differently. Sunset silent email addresses whenever you feel like it, low stakes. But set a standing rule for SMS: 12 months of silence flags a number for re-permission, 18 months means stop blasting it until it re-confirms.
If you want to run that first re-permission pass, the scrub-then-confirm flow above is the whole playbook. You can see current per-segment and scrub pricing on the Ready product page, or start with 20 free texts and clean up one aging cohort before your next big send.