Migrate from Resend.
Same developer-first DX. Same disclosure-based AUP. New: typed reply events, native injection scanning, per-agent reputation, MCP-native distribution. ~30 minutes of changes, mostly inbound-side.
You keep what Resend got right. You stop doing the inbound work yourself.
Resend handles the send side well. Moving to mails.ai keeps that. What changes is the reply side. You don’t write your own classifier anymore. Intent, entities, and injection scores come back pre-computed.
- Send-side is a near-drop-in. Both APIs run on AWS SES under the hood. SDK shape is similar; method names differ.
- Inbound goes from raw → typed. Stop calling your own classifier on every reply.
event.intentis pre-computed. - Pricing is parallel at low volume, beats Resend on parses at scale. Pro $20 = 50K sends + 50K parses (Resend Pro $20 = 50K sends only, parses are DIY).
- Both are transactional-email AUPs — send to recipients you have a relationship with. We modeled ours on theirs.
Send + receive, side by side.
// Resend — send + inbound webhook with raw body parsing
import { Resend } from "resend";
const resend = new Resend(process.env.RESEND_KEY);
await resend.emails.send({
from: "sarah@yourcompany.com",
to: "user@example.com",
subject: "Demo",
html: "<p>...</p>",
});
// Inbound webhook posts the raw message — you parse it yourself.
app.post("/webhook/inbound", async (req, res) => {
const { text, from, subject } = req.body;
const intent = await myClassifier(text); // your own LLM call
const entities = await myEntityExtractor(text); // your own LLM call
// ...
});// Mails.ai — send + typed reply event
import { mails } from "@mailsai/sdk";
const agent = mails.agent("sarah", { domain: "yourcompany.com" });
await agent.send({
to: "user@example.com",
subject: "Demo",
body: "...",
});
// Inbound arrives as a typed reply event — classifier output is built-in.
agent.onReply((event) => {
// event.intent => "schedule_demo"
// event.entities => { date, time }
// event.urgency => 0.8
// event.injection_score => 0.02
// event.sender_reputation => 0.91
});What maps to what.
| Resend | Mails.ai | Notes |
|---|---|---|
| POST /emails | POST /v1/messages | Same shape; add agent_id field on Mails.ai for per-agent reputation. |
| GET /domains | Custom domains — Phase 2 | Today every agent sends from a shared @{slug}.mails.ai identity (no DNS setup). Custom-domain verification (DKIM/SPF/DMARC) ships in Phase 2. |
| Inbound webhook (raw) | GET /v1/events + webhook | Mails.ai inbound is pre-classified into a structured reply event — no parsing in your code. |
| GET /audiences | (n/a — different product) | Resend Marketing is a separate product. Mails.ai is single-product transactional API + agent inbox primitive. If you use Resend Audiences for broadcast, keep using it; Mails.ai doesn't compete on broadcast. |
| Stripe billing (per-1K rates) | Stripe billing — Metered tier (coming soon: $0.001/send + $0.002/inbound (+$0.003 opt-in classify)) | On Metered (coming soon), sends bill at commodity rate (matches Resend's effective per-1K); parses at LLM-value rate (covers built-in classifier cost). |
The questions engineers actually ask.
Will my domain verification carry over?
No — DKIM CNAMEs are provider-specific. Add the three Mails.ai-side CNAMEs alongside your existing Resend records during the dual-run phase; remove the Resend records after you're confident your traffic has fully cut over. SPF / DMARC TXT records get amended (not replaced) so both providers can sign simultaneously during transition.
Can I keep using Resend for broadcast and Mails.ai for transactional?
Yes — they're different products. Resend Marketing handles audience broadcasts; Mails.ai handles agent-triggered transactional and inbox automation. Keep both; route per use case.
What about the disclosure / unsub rules?
Same as Resend's AUP — every send must include a valid sender address, your company name, an explicit disclosure of why you're contacting the recipient, and an unsubscribe mechanism honored within 7 days. Organizational addresses only (not personal). Auto-suspension at 0.3% complaint rate kicks in regardless. We modeled our AUP on Resend's because we like how they handle it.
Can I evaluate Mails.ai without paying — staying under the 3K free-tier cap?
Yes — both free tiers are 3K events/month, so a dual-run evaluation fits inside the free tier on both sides. As you scale, Mails.ai Pro $20 = 50K sends + 50K parses (Resend Pro $20 = 50K sends only), so the value-add is the included parse capacity for the same monthly dollar.
Built for agents.
Self-serve in minutes.
Public API opens Q3 2026. Drop ~6 lines into your agent and ship.
$ npm install @mailsai/sdk