Resend

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.

Install

• pip install resend Python

Imports

• resend

  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

'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'