What is the difference between email and SMS marketing?

Email is high-content, low-cost (fractions of a cent per send), and tolerated at higher frequency. SMS is short-form (160 chars), higher cost ($0.005-$0.05 per message), and intolerant of frequency — more than 2-4 messages per week burns subscribers. SMS open rates are 90%+ vs email at 20-30%, but SMS list-building is slower.

Can I send marketing SMS to my email subscribers?

No, not without explicit SMS opt-in. SMS marketing requires separate, explicit consent — TCPA in US, GDPR in EU, and CASL in Canada all distinguish SMS consent from email consent. Sending SMS based on email opt-in is illegal in most jurisdictions. Use double opt-in at SMS signup to document consent.

What is the best platform for email and SMS marketing?

For ecommerce: Klaviyo (best email, solid SMS), Attentive (best SMS, weaker email), Postscript (Shopify SMS specialist + email). For SMB cross-channel: Omnisend, Brevo. For enterprise: Braze, Iterable. Integrated platforms beat separate tools because of attribution and frequency coordination.

How often should I send marketing SMS?

1-2 promotional SMS per week maximum for ecommerce, 1-4 per month for non-promotional sectors. SMS opt-out rates are sensitive to frequency — more than 2 messages/week typically drives 15-30% monthly opt-out. Reserve SMS for the highest-value, most time-sensitive sends; use email for everything else.

What are SMS marketing compliance requirements?

TCPA (US): explicit consent, identifiable sender, STOP/HELP keywords. CTIA guidelines: clear opt-in process, content restrictions for SHAFT topics (sex, hate, alcohol, firearms, tobacco). Carrier rules require 10DLC registration for application-to-person SMS in US. International: similar consent requirements with stricter enforcement in EU under GDPR.

Email + SMS Marketing: Coordinated Multi-Channel Setup

Email and SMS are different channels with different economics, compliance frameworks, and subscriber tolerances. The cluster around email and sms marketing treats them as a coordinated pair — which is correct for execution but only works when you respect the differences.

For ecommerce, SaaS notifications, and time-sensitive marketing, integrated email + SMS programs drive measurably better results than either alone. For most B2B and content-driven sectors, SMS is barely worth the operational overhead. This guide covers when each channel fits, how to coordinate them, and the tools that handle both well.

Channel Economics

Factor	Email	SMS
Cost per send	$0.0001-$0.001	$0.005-$0.05 (US)
Open rate	20-35%	90-98%
CTR	1-3%	15-30%
Frequency tolerance	1-3 per week	1-2 per week (max 4)
Content length	Long-form	160 chars (one segment)
Opt-in friction	Low (email address)	High (phone number)
Compliance complexity	Medium	High (TCPA, carrier rules)

SMS gets opened more, costs more, and burns out faster. Email is cheap, lower engagement per send, but supports higher volume.

When Each Channel Wins

Use SMS for:

Order shipped / delivered alerts
Appointment reminders
2FA codes (transactional, not marketing)
Time-sensitive high-value promotions ("Sale ends in 4 hours")
Back-in-stock notifications for high-demand items
Abandoned cart at 30 minutes (after no email click)
VIP/loyalty member exclusive drops

Use Email for:

Welcome series
Educational content / nurture
Newsletters
Product launches
Lower-urgency promotions
Detailed transactional info (receipts, order confirmations with line items)
Re-engagement campaigns
Post-purchase follow-up sequences

Use Both for:

Major sales events (email first, SMS day-of)
New customer onboarding (email for content, SMS for milestone triggers)
Win-back campaigns (email first, SMS only for highest-value at-risk customers)

SMS Compliance Basics (US Focus)

TCPA Consent

Sending marketing SMS without prior express written consent is a $500-$1,500 per-message violation. Real cases settle for millions. Don't gamble here.

Consent must be:

Explicit ("I agree to receive marketing texts" — not buried in TOS)
Documented (timestamp, IP, opt-in source)
Separate from email consent
For a specific sender (you, not "our marketing partners")

Required Disclosures

Every marketing campaign signup must disclose:

Sender identity
Type of messages
Approximate frequency
Message and data rates may apply
HELP and STOP keywords

Standard opt-in confirmation message format:

[BRAND] Welcome! You'll receive 4-6 msgs/mo.
Reply STOP to cancel, HELP for help.
Msg&data rates may apply.

10DLC Registration

For US application-to-person SMS, you must register your business and use cases through The Campaign Registry (TCR). Required since 2023 by US carriers. Unregistered traffic gets blocked or filtered.

Most SMS platforms (Klaviyo, Attentive, Postscript, Twilio) handle registration. Budget 7-14 days for approval.

International Considerations

Canada (CASL) — explicit consent + identification + unsubscribe
EU (GDPR + ePrivacy) — explicit consent, easy withdrawal, data minimization
UK (PECR) — soft opt-in possible for similar products to existing customers
Australia — explicit consent, opt-out mechanism required

If you send SMS internationally, segment lists by region and apply the strictest applicable rules.

Platforms That Do Both Well

Platform	Email strength	SMS strength	Best for
Klaviyo	Excellent	Good	Ecommerce hybrid
Attentive	Weak	Excellent	SMS-led ecommerce
Postscript	None (integrates Klaviyo)	Excellent	Shopify SMS
Omnisend	Good	Good	SMB ecommerce
Brevo	Decent	Decent	Mixed marketing
Braze	Excellent	Good	Enterprise SaaS
Iterable	Excellent	Good	Enterprise cross-channel

For ecommerce on Shopify, Klaviyo's email + SMS is the most common stack. For larger operations or SMS-first programs, Attentive or Postscript paired with a separate email tool.

Practitioner note: Klaviyo SMS is good. Attentive SMS is better at the marketing automation tier (smarter segmentation for SMS specifically, better template library, deeper carrier relationships). The tradeoff: Klaviyo's email is best-in-class while Attentive's email is an afterthought. If you're SMS-led, Attentive + a separate email tool beats Klaviyo all-in-one.

Sequencing Patterns That Work

Abandoned Cart

T+30 min: Email — "Did you forget something?"
T+4 hr:   SMS — "Still thinking? Use code SAVE10 for 10% off" (only if email not clicked)
T+24 hr:  Email — "Final reminder + maybe a different offer"
T+48 hr:  No SMS (don't burn the channel)

Welcome

T+0:      Email — Welcome + brand story + first offer
T+1 day:  Email — Top products / popular content
T+3 days: SMS — One welcome message, opt-in confirmation if not done
T+7 days: Email — Social proof / reviews

Win-Back

Day 0:    Email — "We miss you" with offer
Day 7:    Email — "Still interested?" with different angle
Day 14:   SMS — Only for highest-value at-risk customers, single attempt
Day 30:   Final email — sunset notice if still no engagement

Order Update Flow (Transactional, Not Marketing)

Order placed:   Email confirmation with line items
Order shipped:  SMS with tracking link + Email with full details
Order delivered: SMS confirmation
Day +5:         Email — Review request

Practitioner note: The biggest SMS mistake I see in ecommerce: sending the same flow to the same person via email AND SMS at the same time. Welcome email + welcome SMS within 5 minutes feels desperate. Stagger by at least 2 hours, ideally use one channel as primary for each trigger.

Cost Modeling

For a 100K-subscriber ecommerce list:

Email-only program:

4 sends/week × 100K = 400K sends/week
1.6M sends/month
Klaviyo cost: ~$700/month

Email + SMS program (50K SMS subscribers):

Same email cost: ~$700/month
2 SMS/week × 50K = 100K SMS/week, 400K SMS/month
SMS cost at $0.01/msg (US average): $4,000/month
Total: ~$4,700/month

SMS economics work only when conversion rates and AOV justify the per-message cost. For a $50 AOV product with 5% SMS CTR and 5% conversion, you're paying $0.01 for $0.125 in revenue per send — solidly profitable. For a $5 AOV product, harder math.

Authentication and Deliverability

SMS deliverability is mostly about carrier reputation and 10DLC registration — handled by your SMS platform. You don't configure DNS for SMS.

Email deliverability is on you. Authentication (SPF, DKIM, DMARC) on the email sending domain. See email deliverability guide and Gmail/Yahoo bulk sender requirements.

What Not to Do

Send marketing SMS without explicit opt-in. Massive legal risk.
Send the same content via both channels back-to-back. Feels spammy.
Use SMS for low-urgency newsletter content. Email is for context.
Skip 10DLC registration. Carriers will throttle or block you.
Treat SMS as "free reach." It's the most expensive channel per send, use it sparingly.

If you need help building an integrated email + SMS program with proper compliance and deliverability setup, book a consultation. I work with ecommerce and SaaS teams on multi-channel architecture and the email infrastructure underneath.

Sources

v1.0 · May 2026