Customer.io vs Substack
Customer.io is a email marketing platform while Substack is a newsletter platform. Customer.io has been around since 2012, giving it a 5-year head start over Substack (founded 2017). Customer.io starts at $100/mo, while Substack is free. Their pricing is not measured the same way, so we don't rank them on price. Substack offers a free plan (Unlimited subscribers, unlimited emails, all core features free — Substack only charges when you earn), while Customer.io does not. Customer.io has the edge with marketing automation, A/B testing, SMS marketing.
Quick Verdict
Customer.io wins on deliverability, integrations.
Substack wins on free tier.
Best for most users: Customer.io (product led saas companies with event driven messaging needs).
Customer.io
Behavioral messaging platform for product-led SaaS and tech companies
Customer.io is a behavioral messaging platform built for product-led SaaS companies that need to trigger automated emails, SMS, push notifications, and in-app messages based on real-time user events. Its visual workflow builder and Liquid templating provide deep personalization, while the built-in Data Pipelines act as a lightweight CDP. Trusted by 8,000+ companies including Notion and Segment, it starts at $100/month for 5,000 profiles.
Substack
The newsletter platform where writers build independent media businesses
Substack is the dominant newsletter platform that uniquely combines free publishing tools with a 10% revenue-share model, letting writers launch subscription-based media businesses with zero upfront cost. Beyond newsletters, it has evolved into a full creator ecosystem with podcasts, video, livestreaming, Notes (microblogging), and community Chat, backed by a powerful built-in discovery network that helps writers find audiences organically.
Feature Comparison
| Feature | Customer.io | Substack |
|---|---|---|
| Rating | 4.4/5 | 4.4/5 |
| Starting Price | $100/mo | Free |
| Free Plan | No free plan | Unlimited subscribers, unlimited emails, all core features free — Substack only charges when you earn |
| Founded | 2012 | 2017 |
| Email Templates | 30 | 1 |
| Integrations | 150 | 0 |
| Deliverability Rate | 96% | 95% |
| Marketing Automation | Yes | No |
| A/B Testing | Yes | No |
| Landing Pages | No | No |
| Segmentation | Yes | No |
| Drag & Drop Editor | Yes | No |
| SMS Marketing | Yes | No |
| Ecommerce Features | No | No |
| API Access | Yes | No |
| Multi-Language | Yes | No |
| Web Push Notifications | Yes | No |
| Live Chat | No | No |
| Advanced Analytics | Yes | No |
Customer.io: Pros & Cons
Pros
- + Powerful visual workflow builder with real-time event-based triggers for behavioral automation
- + Omnichannel messaging across email, SMS, push notifications, in-app, and webhooks in one platform
- + Built-in Data Pipelines that serve as a lightweight CDP, unifying web, mobile, and backend data
- + Segment builder is intuitive enough for marketers without requiring dedicated engineering support
- + Startup Program offers up to 12 months free for qualifying early-stage companies
Cons
- − Essentials plan starts at $100/month for only 5,000 profiles — expensive for small teams
- − Steep learning curve for non-technical users, especially with Liquid templating syntax
- − Pricing scales aggressively past 10K profiles with significant jumps between plan tiers
- − Template editor feels restrictive for highly custom-coded email layouts
- − Searching for past messages and editing templates can be unintuitive and slow
Substack: Pros & Cons
Pros
- + Completely free to start with no upfront costs — zero barrier to entry with all core publishing features available immediately
- + Built-in audience discovery network with Recommendations and Notes driving organic subscriber growth (users report gaining 1,000+ subscribers through Recommendations alone)
- + True content ownership: creators can export their full subscriber list and content at any time to migrate elsewhere
- + Multimedia platform supporting newsletters, podcasts, video, livestreaming, Notes, and Chat communities in a single integrated experience
- + Strong reader engagement with genuine community interaction through comments, Chat, and Notes — higher engagement rates than typical social media platforms
Cons
- − The 10% platform fee plus Stripe's ~2.9% + $0.30 per transaction creates a 13-16% total take rate that becomes very expensive at scale (e.g., $1,300-$1,600/month on $10K revenue)
- − No email marketing automation, segmentation, A/B testing, or advanced personalization — all subscribers receive identical emails with no conditional logic
- − No public API and zero native third-party integrations — cannot connect to CRMs, e-commerce platforms, Zapier, or other marketing tools
- − Limited design customization with a single standardized template — no drag-and-drop editor, no custom HTML, and minimal branding options
- − Platform can remove content or delete accounts without notice, and customer support is difficult to reach for issue resolution
The Verdict
Customer.io and Substack are closely matched — both score within 0.0 points of each other in our overall rating. Your decision should come down to specific needs rather than overall quality. On deliverability, Customer.io reports 96% compared to 95% for Substack — a meaningful difference if inbox placement is critical for your campaigns.
| Criterion | Weight | Customer.io | Substack |
|---|---|---|---|
| Starting Price | 30% | $100/mo | Free |
| Deliverability | 25% | 96% Winner | 95% |
| Rating | 25% | 4.4/5 | 4.4/5 |
| Integrations | 10% | 150 Winner | 0 |
| Free Tier | 10% | No | Yes Winner |
Weights determine how much each criterion counts toward the final score. See full methodology
Choose Customer.io if…
- + You need SMS marketing
- + You need marketing automation
- + You need API access for custom integrations
- + You need A/B testing
Choose Substack if…
- + You need a free plan to get started
- + You're a independent writers and journalists
- + You're a newsletter creators monetizing through paid subscriptions