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To use MailChannels Outbound Filtering, you configure your mail transfer agent (MTA) to use MailChannels as a smart host—also called an SMTP relay. Instead of delivering email directly to recipients, your mail server hands every outbound message to MailChannels, which filters it, manages IP reputation, and delivers it on your behalf.

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Before you begin

You need:
  • A MailChannels Outbound Filtering account
  • Your SMTP username (same as “Account ID” in the Host Console under Settings > Account > SMTP Passwords)
  • An SMTP password (create one in the Host Console if you haven’t already)
  • Access to your mail server’s configuration
TLS encryption is required for all connections from your mail server to MailChannels. Do not configure your MTA to use legacy SSL-mode encryption.

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Connection details

Use these settings when configuring your MTA:
SettingValue
Relay hostsmtp.mailchannels.net
Port25 (preferred), 587 (STARTTLS), or 2525
EncryptionTLS (STARTTLS)
AuthenticationSMTP AUTH with your MailChannels username and password
If port 25 is blocked in your network or by your hosting provider, use port 587 with STARTTLS or port 2525 as a fallback.

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Set up your mail server

1

Get your credentials

Log in to the Host Console and go to Settings > Account > SMTP Passwords. Your SMTP username (Account ID) is shown on this page. If you don’t have a password yet, create one here.
2

Configure the smart host

In your MTA configuration, set the relay or smart host to smtp.mailchannels.net. The exact setting name varies by MTA — refer to the guide for your specific mail server below.
3

Enable SMTP authentication

Configure your MTA to authenticate to smtp.mailchannels.net using the username and password from the Host Console. Use PLAIN or LOGIN SASL mechanisms over a TLS-encrypted connection.
4

Enable TLS

Set your MTA to require TLS when connecting to the MailChannels relay. Connections without TLS are rejected.
5

Set up SPF records

Update your domain’s SPF records to authorize MailChannels to send on your behalf. Without this step, receiving mail servers may reject your messages. See Set up SPF records for instructions.
6

Set up monitors

After your mail server is relaying through MailChannels, configure monitors in the Host Console so you’re notified when a compromised sender is detected. See Monitors and alerts.
Monitors are only available in Standard Plans and above

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Sender identification headers

To help MailChannels track individual senders accurately, your MTA should add identification headers to each message. These headers let the system attribute email to a specific user, application, or script — which is essential for isolating compromised accounts without blocking everyone else.
Add X-AuthUser headerThis X-AuthUser header often contains the authenticated sender address but can contain any unique identifier which you can use to locate the responsible sending entity.
The MTA-specific configuration guides contain details on how to insert the X-AuthUser header.

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MTA-specific setup guides

Choose the guide that matches your mail server:

Postfix

Configure Postfix relayhost and SASL authentication for MailChannels.

cPanel / Exim

Set up MailChannels as the smart host in WHM and cPanel environments.

Exim (advanced)

Advanced Exim configuration for custom routing and per-domain relay settings.

Microsoft Exchange

Configure Exchange 2019 to send outbound mail through MailChannels.

Sendmail

Configure Sendmail with SASL authentication and smart host routing.

Zimbra

Route outbound mail through MailChannels and add X-AuthUser headers in Zimbra.

DirectAdmin

Configure Exim on DirectAdmin servers to relay through MailChannels.

SmarterMail

Set up an outgoing gateway and authenticated sender headers in SmarterMail.
For a full list of supported mail servers, see the MTA Setup section in the sidebar. If your MTA is not listed, look for “smart host” or “relay host” configuration options in your mail server’s documentation, or contact MailChannels support for guidance.