Skip to main content
This guide walks you through configuring Zimbra to relay all outbound mail through MailChannels Outbound Filtering and adding the X-AuthUser header for per-sender reputation tracking.

​
Prerequisites

  • Root or administrative access to your Zimbra server
  • Your MailChannels SMTP username and password

​
Configure the relay

1

Open Global Settings in the Zimbra Admin Console

Navigate to https://<your-zimbra-server>:7071 and log in with your admin credentials.Go to Configure > Global Settings and select the MTA tab.
2

Set the relay smart host

Configure the following values:
FieldValue
Relay MTA for external deliverysmtp.mailchannels.net
SMTP Port587
TLS encryptionEnabled
Relay Authentication UsernameYour MailChannels SMTP username
Relay Authentication PasswordYour MailChannels SMTP password
Click Save.

​
Add the X-AuthUser header

MailChannels uses the X-AuthUser header to identify the authenticated sender and track per-sender reputation. Messages without this header are treated as forwarded mail and subject to different policies. Zimbra uses Postfix as its MTA, so the header is added via a Postfix sender access map.
1

Add the smtpd_sender_restrictions directive

Open /opt/zimbra/conf/main.cf:
sudo nano /opt/zimbra/conf/main.cf
Add the following line to include the custom header access map:
/opt/zimbra/conf/main.cf
smtpd_sender_restrictions = check_sender_access hash:/opt/zimbra/conf/custom_header
2

Create the custom header file

Create /opt/zimbra/conf/custom_header:
sudo nano /opt/zimbra/conf/custom_header
Add the following line:
/opt/zimbra/conf/custom_header
PREPEND X-AuthUser: ${authenticated_user}
3

Compile the hash database

Postfix requires a compiled hash database from the text file:
sudo postmap /opt/zimbra/conf/custom_header
4

Restart the Zimbra MTA

Apply all changes by restarting the Zimbra MTA service:
sudo /opt/zimbra/libexec/zmmtactl restart

​
Resources

​
Verify the configuration

1

Send a test email

Send a test email from a Zimbra user account to an address you control and confirm it is delivered successfully.
2

Check the X-AuthUser header

Inspect the headers of the received email and confirm that X-AuthUser is present and correctly populated with the authenticated user value.
3

Review the MailChannels Host Console

Log in to your MailChannels Host Console and navigate to Outbound > Log Search. In the transaction log, the senderID (sid=) field should contain your ${authenticated_user} value in the third position.