OpenAI API vs Resend
Frontier models: GPT-5, o-series reasoning, image, audio, embeddings
vs. The email API for developers — built by the Nodemailer team
Pricing tiers
OpenAI API
Free Tier (Trial)
$5 free credit for new accounts. Rate-limited.
Free
Pay-as-you-go
No monthly min. Per-token pricing by model.
$0 base (usage-based)
Usage Tiers (1-5)
Automatic tier promotion based on cumulative spend. Higher tiers = higher rate limits + new model access.
$0 base (usage-based)
Enterprise
Custom. Priority access, SLA, dedicated capacity.
Custom
Resend
Free
3,000 emails/month, 100 emails/day. 1 custom domain. Ideal for side projects.
Free
Pro — 50k
50,000 emails/month. 10 custom domains. Priority support.
$20/mo
Pro — 100k
100,000 emails/month. 10 custom domains.
$35/mo
Scale — 100k+
Tiered from 100k → 2.5M emails/month. Dedicated IP add-on available.
$90/mo
Scale — 2.5M
2.5M emails/month.
$1150/mo
Enterprise
3M+/month, dedicated IP included, SSO, custom contract.
Custom
Free-tier quotas head-to-head
Comparing free-tier on OpenAI API vs free on Resend.
| Metric | OpenAI API | Resend |
|---|---|---|
| custom domains | — | 1 domains |
| emails per day | — | 100 emails/day |
| emails per month | — | 3000 emails/month |
Features
OpenAI API · 12 features
- Assistants API — Stateful assistants with tools, threads, file search.
- Batch API — 50% discount for async processing within 24h.
- Chat Completions API — Classic /v1/chat/completions endpoint.
- Files API — Upload docs for retrieval, fine-tuning, batch.
- Fine-Tuning — Supervised + DPO fine-tuning for GPT-4o, GPT-4.1, GPT-4o-mini.
- Function Calling — JSON-schema tool calling; parallel calls supported.
- Moderation — Safety classifier API (free).
- Prompt Caching — Auto-cache repeated prefixes; 50% cheaper cached hits.
- Realtime API — WebSocket streaming voice + text with low latency.
- Responses API — Stateful conversational API.
- Structured Outputs — Enforced JSON schema compliance.
- Vision — Image input for GPT models.
Resend · 12 features
- Audiences — Contact list management with custom fields.
- Batch Send — Send up to 100 emails in one API call.
- Broadcasts — Bulk email campaigns with audiences, A/B testing, analytics.
- Dedicated IP — Add-on for high-volume senders. Auto warmup.
- Domains — DKIM/SPF/DMARC auto-verification. Per-domain analytics.
- Idempotency — Prevent duplicate sends with Idempotency-Key header.
- Logs + Analytics — Full email logs, delivery heatmap, events table.
- React Email — OSS library (3M+ downloads) to compose emails in React/JSX.
- Scheduled Send — scheduledAt parameter for future delivery.
- Send API — POST /emails endpoint to send. Supports attachments, scheduled send, idempotency…
- Suppressions — Auto-managed bounce + complaint list. API to add/remove.
- Webhooks — Email lifecycle events: sent, delivered, bounced, complained, opened, clicked.
Developer interfaces
| Kind | OpenAI API | Resend |
|---|---|---|
| CLI | — | Resend CLI |
| SDK | openai-dotnet, openai-go, openai-node, openai-python | react-email, resend-go, resend-node, resend-php, resend-python, resend-ruby |
| REST | OpenAI REST API | Resend REST API |
| MCP | OpenAI MCP | — |
| OTHER | Realtime API (WebSocket) | SMTP Relay, Webhooks (Svix) |
Staxly is an independent catalog of developer platforms. Outbound links to OpenAI API and Resend are plain references to their official websites. Pricing is verified against vendor pages at publication time — reconfirm before buying.
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