CLI tool to send bulk emails via Resend's free-tier Marketing/Broadcast API, with Supabase as the tracking database.

Why this tool exists

Resend's transactional email limits (100/day, 3000/month on the free tier) are too restrictive for large contact lists. The Marketing/Broadcast API has much higher limits but caps audiences at 1000 contacts and 3 segments. This tool works around those limits by batching: it adds ~100 contacts to a segment, sends a broadcast, removes them, and repeats — tracking everything in Supabase.

How it works

CSV files ──► Supabase (import) ──► Resend Broadcast (send) ──► Supabase status update

The batching process

Because Resend limits audiences to 1000 contacts, the tool sends emails in small batches (~100 contacts). For each batch:

1. Add contacts to the Resend segment (with their properties including unsubscribe_token)
2. Create a broadcast using your Resend template
3. Send the broadcast to the segment
4. Wait for delivery confirmation (polls broadcast status)
5. Clean up contacts — newly created contacts are fully deleted from Resend; contacts that already existed before the batch are only removed from the segment (not deleted)
6. Update Supabase — mark recipients as sent

This cycle repeats for every batch until all pending recipients are processed. The process is resumable: if interrupted, re-run the same command and it picks up where it left off.

Unsubscribe handling

Because contacts are removed from Resend after each batch, Resend cannot manage unsubscribe status for you. The init command automatically deploys a Supabase Edge Function that handles unsubscriptions — no external hosting required.

Each contact gets a unique unsubscribe_token (UUID). In your Resend email template, add the unsubscribe link printed at the end of init:

<a href="https://<your-project-ref>.supabase.co/functions/v1/unsubscribe?token={{{contact.unsubscribe_token}}}">Unsubscribe</a>

When a recipient clicks the link, the Edge Function updates their unsubscribed_at timestamp in Supabase and shows a confirmation page. The send command automatically skips any recipient where unsubscribed_at is set.

Prerequisites

• Node.js 22+
• Supabase project + personal access token (Account > Access Tokens)
• Resend account with API key (an audience is created automatically during init)
• Resend email template created beforehand (see below)

Setup

1. Install

npm install -g @pekno/rebatch

2. Create your Resend template

Before using this tool, create an email template in the Resend dashboard (Templates section). This template is what will be sent to your contacts.

In the template, you can use Resend's contact properties as variables:

• {{{contact.first_name}}} — recipient's first name
• {{{contact.last_name}}} — recipient's last name
• {{{contact.company_name}}} — recipient's organization
• {{{contact.unsubscribe_token}}} — unique unsubscribe UUID (see Unsubscribe handling)

You will reference this template by its exact name when running the send command.

3. Configure

rebatch init

The init command will:

1. Prompt for your Resend API key
2. Automatically create (or reuse) a rebatch audience in Resend
3. Connect to Supabase via your access token and let you pick a project
4. Auto-fetch the project's API keys
5. Create the email_recipients table
6. Deploy the unsubscribe Edge Function
7. Print the unsubscribe link to paste in your Resend template

Config location:

• Windows: %APPDATA%/rebatch/config.json
• macOS: ~/Library/Application Support/rebatch/config.json
• Linux: ~/.config/rebatch/config.json

You only need two credentials:

Field	Where to find it
resendApiKey	Resend dashboard > API Keys
supabaseAccessToken	Supabase dashboard > Account > Access Tokens

Usage

Import contacts (CSV to Supabase)

# Preview what will be imported
rebatch import my-group --csv ./contacts.csv --dry-run

# Import for real
rebatch import my-group --csv ./contacts.csv

Imports contacts into the email_recipients Supabase table. Skips duplicates, invalid emails, and contacts already present in the Resend segment.

Expected CSV columns: email, firstname, lastname (configurable via csvColumns in config). The CSV reader auto-detects comma and semicolon delimiters.

Send emails (Supabase to Resend Broadcast)

# Preview batches and recipients
rebatch send my-group --template "My Template Name" --dry-run

# Send for real
rebatch send my-group --template "My Template Name"

Resumable: if interrupted, re-run the same command. Only pending and failed recipients are processed.

Check status

rebatch status my-group

Shows total, pending, sent, failed, and unsubscribed counts with a progress bar.

Delete a group

rebatch delete my-group

Deletes all recipients in a group from Supabase (with confirmation prompt).

Show config path

rebatch config

Configuration reference

Field	Default	Description
resendApiKey	—	Resend API key
segmentId	—	Resend audience ID (auto-created during init)
supabaseAccessToken	—	Supabase personal access token (used during init)
supabaseUrl	—	Supabase project URL (auto-fetched)
supabaseServiceKey	—	Supabase service role key (auto-fetched)
fromEmail	—	Sender (e.g., "Name <you@example.com>")
replyTo	—	Reply-to email address
batchSize	100	Contacts per batch
pollIntervalMs	5000	Broadcast status poll interval
pollTimeoutMs	300000	Max wait for broadcast delivery (5 min)
rateLimitDelayMs	600	Delay between API calls (ms)
csvColumns	—	Maps CSV headers to fields

Rate limiting

Resend enforces a 2 requests/second limit. The rateLimitDelayMs config value (default 600) controls the minimum wait between API calls. If a 429 is still received, the tool automatically retries with increasing backoff (up to 5 retries).

Estimated runtime

Runtime depends on your contact list size. Each batch of 100 contacts takes ~3-4 minutes (adding contacts, sending, polling, removing). For example, ~6500 contacts = ~65 batches = ~4 hours. The process can run unattended.

Testing

npm test                # run all 64 tests
npm run test:coverage   # run with coverage report

All external APIs are mocked — no credentials needed. Tests cover CSV parsing, Resend API retry/rate-limiting, Supabase query logic, the batch orchestration loop, and CLI argument validation.

See TEST.md for full documentation of every test case with links to source.

License

MIT