AISend vs Customer.io
A detailed comparison of AISend and Customer.io for sending transactional emails. Which email API is right for your application?
Overview
Both AISend and Customer.io provide email APIs for sending transactional emails from applications. AISend differentiates itself with AI-powered multi-provider routing, deliverability scoring, and send time optimization. While Customer.io routes through a single provider, AISend intelligently selects the best provider (AWS SES, Postmark, or SMTP) for each email based on real-time deliverability data.
Features comparison
Key differences between AISend and Customer.io: API design and developer experience, deliverability features, analytics and monitoring, custom domain support, webhook event tracking, and pricing structure. AISend includes AI features that Customer.io doesn't offer: intelligent provider routing for higher deliverability, content scoring that catches spam triggers before sending, and send time optimization that improves engagement rates.
Pricing
Pricing is a major factor when choosing an email API. Compare the free tiers, per-email costs at different volumes, and what features are included in each plan. AISend offers 1,000 emails/month free with all AI features included. Pro plans start at $29/month for 25,000 emails. Unlike Customer.io, AISend includes AI deliverability optimization, multi-provider routing, and content scoring at every pricing tier — even the free plan.
Which should you choose?
Choose AISend if you want the highest possible deliverability through AI-powered multi-provider routing, content scoring, and send time optimization. Choose Customer.io if you're already deeply integrated and don't need AI features. AISend's API is Resend-compatible, making migration straightforward when you're ready for AI-powered delivery.