# Customer.io (SMTP)

> Send Customer.io campaigns and transactional email through MailBlastr over SMTP.

Customer.io lets you bring your own SMTP server for sending email. Add MailBlastr as a custom SMTP server so your campaigns and transactional messages are delivered through MailBlastr and tracked in your dashboard.

## Prerequisites

- A MailBlastr [API key](https://www.mailblastr.com/docs/api-keys/overview).
- A [verified domain](https://www.mailblastr.com/docs/domains/managing) to send from.

## 1. Get your SMTP credentials

You'll configure Customer.io with the following MailBlastr credentials:

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `Host` | string | No | `smtp.mailblastr.com` |
| `Port` | number | No | `465` (implicit TLS) or `587` (STARTTLS). |
| `Username` | string | No | `mailblastr` |
| `Password` | string | No | Your API key, e.g. `mb_xxxxxxxxx`. |

## 2. Add MailBlastr as a custom SMTP server

After logging into [Customer.io](https://customer.io), enable the SMTP integration:

1. **Workspace Settings** — Go to **Settings > Workspace Settings**.
2. **Email** — Open the **Messaging** tab and select **Email**.
3. **Custom SMTP** — Select the **Custom SMTP** tab and click **Add Custom SMTP Server**.
4. **Other SMTP** — Select **Other SMTP** and click **Continue to set up**.
5. **Paste credentials** — Enter the MailBlastr host, port, username (`mailblastr`), and password (your API key) from the section above.

> **Warning:** Make sure your sending address in Customer.io is on a domain you have verified in MailBlastr, otherwise sends will be rejected.