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AutoSend x Customer.io
Customer.io is a messaging platform for marketing, transactional emails, push notifications, and in-app messages. By default, Customer.io uses its built-in email service, but you can configure it to use AutoSend SMTP for better deliverability and email tracking.

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Prerequisites

Verified Domain

Make sure you have a verified domain added in AutoSend to send emails from.

API Key

Create a new API key for SMTP authentication or use the existing one.

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Configuration

1

Navigate to Email Settings

  1. Log in to your Customer.io Dashboard
  2. Go to Settings > Workspace Settings
  3. Click on Email
Supabase Step 1
2

Add Custom SMTP Server

  1. Click on Custom SMTP
  2. Select Add Custom SMTP Server
Supabase Step 2
3

Select SMTP Provider

Select Other SMTP as your provider type and click Continue to set up.
Supabase Step 3
4

Enter SMTP Credentials

Fill in the following settings:
FieldValue
Addresssmtp.autosend.com
Port587 (or 465 for implicit TLS)
AuthenticationSelect Plain
Usernameautosend
PasswordYour AutoSend API key (AS_xxx)
Supabase Step 1
Customer.io does not support port 25. Use port 587, 465, or 2525 instead.
Click Finish set up to save your configuration.
5

Add a Sending Domain

Before sending emails, add a sending domain in Customer.io that matches your verified domain in AutoSend.
  1. Go to Settings → Workspace Settings → Email
  2. Under Sending Domains, add your domain (e.g., yourdomain.com)
Supabase Step 5
6

Send a Test Email

Create a test campaign or broadcast to verify your SMTP configuration is working correctly.You can also check the Email Activity dashboard to verify the email was sent through AutoSend.

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Troubleshooting

  • Verify your SMTP credentials are correct - Check that your sender email domain is verified in AutoSend - Ensure you’ve added a sending domain in Customer.io - Check Customer.io’s delivery logs for SMTP connection errors
  • Double-check your API key is correct - Ensure you’re using autosend as the username - Verify your API key is active in the AutoSend dashboard
  • Verify the server address is smtp.autosend.com - Try using port 465 or 2525 if port 587 fails - Remember that port 25 is not supported by Customer.io
  • Ensure your domain has proper DNS records (SPF, DKIM, DMARC) - Use a professional sender name and address - Check your domain reputation in AutoSend

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Next Steps

Verify Your Domain

Set up SPF, DKIM, and DMARC for better deliverability

Email Activity

Monitor your email delivery and engagement

Webhooks

Set up webhooks to track email events in real-time

SMTP Introduction

Learn more about AutoSend SMTP configuration