When setting up server alerts via Postfix, many administrators want to customize both the sender identity and email subject for better identification. The default configuration often shows unhelpful information like:

From: root@hostname (root)
Subject: Alert from hostname

We want to transform this into more professional-looking emails with:

From: zeus@example.com (Zeus)
Subject: [Zeus.domain] - Disk Space Alert

The first part is handled through smtp_generic_maps in /etc/postfix/main.cf:

smtp_generic_maps = hash:/etc/postfix/generic

Then create/edit /etc/postfix/generic:

root@zeus zeus@example.com
@zeus.localdomain @example.com

Run postmap /etc/postfix/generic and reload Postfix.

To change the displayed name from "root" to "Zeus", modify /etc/postfix/main.cf:

smtp_header_checks = regexp:/etc/postfix/header_checks

Create /etc/postfix/header_checks:

/^From:.*\$(.*)\$/ REPLACE From: $1 <${sender}>
/^From:.*/ REPLACE From: Zeus <${sender}>

Run postmap /etc/postfix/header_checks and reload Postfix.

For automatic subject prefixing, add to /etc/postfix/main.cf:

smtp_header_checks = regexp:/etc/postfix/header_checks

Then append to your existing header_checks file:

/^Subject:(.*)/ REPLACE Subject: [Zeus.domain] - $1

Send a test email from the server:

echo "Test message" | mail -s "Test Subject" your@email.com

You should receive an email with headers like:

From: Zeus <zeus@example.com>
Subject: [Zeus.domain] - Test Subject

For multiple servers, use a script to generate dynamic header checks. Create /usr/local/bin/update_header_checks:

#!/bin/bash
HOSTNAME=$(hostname)
DOMAIN="example.com"

cat > /etc/postfix/header_checks << EOF
/^From:.*/ REPLACE From: $HOSTNAME <${sender}>
/^Subject:(.*)/ REPLACE Subject: [$HOSTNAME.$DOMAIN] - $1
EOF

postmap /etc/postfix/header_checks
systemctl reload postfix

Make it executable and run it whenever hostnames change.

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When setting up server alerts through Postfix, many administrators encounter an issue where outgoing emails show unwanted default values in the From header. The default configuration often displays:

From: root@hostname (root)

When what we really want is something more professional like:

From: zeus@example.com (Zeus Server)
Subject: [Zeus] Disk Usage Alert

To achieve this, we need to modify several Postfix configuration files. Here's the complete solution:

# /etc/postfix/main.cf
myhostname = zeus.example.com
smtp_generic_maps = hash:/etc/postfix/generic
header_checks = regexp:/etc/postfix/header_checks

Create or edit /etc/postfix/generic:

# /etc/postfix/generic
root@zeus   zeus@example.com
@localhost  @example.com

Then compile the map:

postmap /etc/postfix/generic

For the sender name modification, create /etc/postfix/header_checks:

# /etc/postfix/header_checks
/^From:.*$root$/    REPLACE From: zeus@example.com (Zeus Server)
/^Subject:/          PREPEND [Zeus] 

Then compile the header checks:

postmap /etc/postfix/header_checks

After making these changes, restart Postfix and test with:

systemctl restart postfix
echo "Test message" | mail -s "Test Subject" your@email.com

For more granular control over different services, consider using separate header checks:

# For cron jobs
/^From:.*$root$/    REPLACE From: cron@example.com (Cron Daemon)

# For backup scripts
/^From:.*$root$/    REPLACE From: backup@example.com (Backup System)

• Check mail logs: tail -f /var/log/mail.log
• Verify header processing: postconf -n
• Test header checks: postmap -q - regexp:/etc/postfix/header_checks < test_email.eml