Resend

2.23.0 verified Tue May 12 auth: yes python install: verified quickstart: verified

Official Python SDK for the Resend transactional email API. Active, frequently updated. v2.0 (May 2024) added TypedDict-based type hinting. Module-level api_key pattern is the primary auth method. No class instantiation — all methods are called as class methods on resend.Emails, resend.Contacts, etc.

pip install resend

Common errors

error ModuleNotFoundError: No module named 'resend' ↓

cause The 'resend' package is not installed in your current Python environment.

fix

pip install resend

error resend.exceptions.ResendError: {'name': 'unauthorized', 'message': 'Unauthorized'} ↓

cause The Resend API key is either missing, incorrect, or not properly set before making an API call.

fix

Set resend.api_key with a valid API key, preferably from an environment variable: import os; resend.api_key = os.environ.get("RESEND_API_KEY")

error AttributeError: module 'resend' has no attribute 'send' ↓

cause The `send` method is not directly available on the top-level `resend` module; it must be called via the `resend.Emails` class.

fix

Call the method on the correct class: resend.Emails.send(...)

error resend.exceptions.ResendError: {'message': 'The `from` field is required.', 'name': 'missing_required_field', 'statusCode': 422} ↓

cause A required field (like `from`, `to`, or `subject`) is missing or empty in the dictionary payload for the email.

fix

Ensure all mandatory fields (from, to, subject, html or text) are present and correctly populated in the email payload dictionary.

Warnings

gotcha No client class to instantiate — resend.api_key is set at the module level, then all API calls are made as class methods (resend.Emails.send(), resend.Contacts.list(), etc.). Code from other SDKs that tries to instantiate a client object fails. ↓

fix import resend; resend.api_key = 'YOUR_KEY'; resend.Emails.send(params)

gotcha The 'to' field must always be a list, even for a single recipient. Passing a string raises a validation error. ↓

fix 'to': ['user@example.com'] # not 'to': 'user@example.com'

gotcha The 'from' field must use a domain verified in the Resend dashboard. Using unverified domains or personal email addresses returns 403. The address 'onboarding@resend.dev' works only in testing with the test API key. ↓

fix Verify your domain at resend.com/domains before sending. Format: 'Name <email@yourdomain.com>'

gotcha Module-level api_key is global state — in multi-tenant or async applications with different API keys, setting resend.api_key is not thread-safe. Concurrent requests may use the wrong key. ↓

fix For multi-key scenarios, serialize key setting + API call, or use separate processes/containers per API key.

gotcha Pip warnings detected in the test output, indicating 'Running pip as root' which can cause permission issues, and an 'outdated pip version'. These are environment-specific warnings during package management, not direct failures related to the resend library's functionality. ↓

fix It is recommended to use a virtual environment for pip operations (e.g., `python -m venv .venv && source .venv/bin/activate`) and to keep pip updated (`pip install --upgrade pip`).

Install compatibility verified last tested: 2026-05-12

python os / libc status wheel install import disk

3.10 alpine (musl) - - 0.65s 22.3M

3.10 slim (glibc) - - 0.46s 23M

3.11 alpine (musl) - - 0.87s 24.5M

3.11 slim (glibc) - - 0.72s 25M

3.12 alpine (musl) - - 0.73s 16.2M

3.12 slim (glibc) - - 0.73s 17M

3.13 alpine (musl) - - 0.72s 15.9M

3.13 slim (glibc) - - 0.71s 16M

3.9 alpine (musl) - - 0.64s 21.6M

3.9 slim (glibc) - - 0.51s 22M

Imports

resend

wrong

from resend import Resend
client = Resend(api_key='...')

correct

import resend
import os

resend.api_key = os.environ['RESEND_API_KEY']

params: resend.Emails.SendParams = {
    'from': 'Acme <onboarding@resend.dev>',
    'to': ['user@example.com'],
    'subject': 'Hello',
    'html': '<strong>Hello!</strong>'
}
email = resend.Emails.send(params)
print(email['id'])

No class instantiation — set resend.api_key globally, then call class methods directly. There is no Resend() client object.

Quickstart verified last tested: 2026-05-12

'from' field must use a verified domain. Use 'onboarding@resend.dev' only for testing. The 'to' field must be a list even for single recipients.

import os
import resend

resend.api_key = os.environ['RESEND_API_KEY']

params: resend.Emails.SendParams = {
    'from': 'Acme <onboarding@resend.dev>',
    'to': ['delivered@resend.dev'],
    'subject': 'Hello from Resend',
    'html': '<strong>It works!</strong>'
}

email = resend.Emails.send(params)
print(email['id'])  # e.g. '49a3999c-0ce1-4ea6-ab68-b08b6e9a5fe2'