When dealing with Postfix SMTP authentication through virtual mailboxes (MySQL backend), you might encounter situations where you need to trace which authenticated user account was used to relay a specific email. The standard mail headers often don't reveal this crucial information directly.

First, ensure your Postfix logging includes SASL authentication details. Add this to your main.cf:

# Enable detailed SASL logging
debug_peer_list = 0.0.0.0/0
debug_peer_level = 2

Assuming your virtual mailbox setup looks like this in main.cf:

virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-alias-maps.cf

Check these log files for authentication traces:

• /var/log/mail.log
• /var/log/auth.log
• /var/log/syslog

Look for entries containing 'sasl_method=LOGIN' or similar. Example log entry:

Jul  3 05:42:59 ourserver postfix/smtpd[12345]: ABC123456: client=c-76-109-241-139.hsd1.fl.comcast.net[xx.109.xxx.139], sasl_method=LOGIN, sasl_username=realuser@domain.com

If logs don't show the username, query your mailbox database:

SELECT username FROM mailbox WHERE username IN 
(SELECT name FROM aliases WHERE destination LIKE '%realuser@domain.com%')
UNION
SELECT username FROM mailbox WHERE username = 'realuser@domain.com';

Create a shell script to parse logs for specific message IDs:

#!/bin/bash
MSGID="7BA184B4AD4"
grep "$MSGID" /var/log/mail.log | grep sasl_username

For future messages, add this to main.cf to include auth info in headers:

smtpd_sasl_authenticated_header = yes

If logs are missing authentication info:

1. Verify logrotate isn't compressing logs too aggressively
2. Check syslog filters aren't dropping auth messages
3. Ensure proper SELinux permissions for Postfix logging

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When troubleshooting email delivery issues or investigating potential abuse cases, determining which authenticated user account was used to send a message through Postfix is critical. With a MySQL-based virtual mailbox setup, we need to examine multiple system components:

# Key components to investigate:
1. Postfix SMTP authentication logs
2. MySQL virtual_users table
3. SASL authentication mechanisms
4. Header analysis techniques

First, verify your Postfix and SASL logging configuration. Add these to /etc/postfix/main.cf:

# Enhanced logging for SMTP authentication
debug_peer_list = xx.109.xxx.139
debug_peer_level = 2
smtpd_sasl_authenticated_header = yes

Search your mail logs (typically /var/log/mail.log) for the message ID 7BA184B4AD4:

grep '7BA184B4AD4' /var/log/mail.log | grep -i 'sasl_username'

This should reveal lines like:

postfix/smtpd[1234]: 7BA184B4AD4: client=c-76-109-241-139.hsd1.fl.comcast.net[xx.109.xxx.139], sasl_method=LOGIN, sasl_username=actualuser@domain.com

If logs don't show the SASL username, query your MySQL virtual users table directly. First identify the connecting IP's timestamp:

SELECT * FROM postfix_log 
WHERE client_ip = 'xx.109.xxx.139' 
AND timestamp BETWEEN '2012-07-03 05:42:00' AND '2012-07-03 05:43:00';

Then cross-reference with your virtual_users table:

SELECT * FROM virtual_users 
WHERE id = (SELECT user_id FROM postfix_log WHERE message_id = '7BA184B4AD4');

The ESMTPA in your Received header confirms authentication occurred. While the header shows "User", the actual authenticated username would be in logs. You can add header checks to /etc/postfix/main.cf:

smtpd_sasl_authenticated_header = yes
header_checks = regexp:/etc/postfix/header_checks

Create /etc/postfix/header_checks with:

/^Received:.*with ESMTPA/ PREPEND X-Authenticated-User: $sasl_username

Implement these changes to better track authenticated senders:

# In main.cf:
always_add_missing_headers = yes
smtpd_sasl_exceptions_networks = 
smtpd_sasl_security_options = noanonymous

And create a log processor script (log_analyzer.php):

<?php
$log = file_get_contents('/var/log/mail.log');
preg_match_all('/message-id=([A-Z0-9]+).*sasl_username=([^\s]+)/', $log, $matches);
$messageMap = array_combine($matches[1], $matches[2]);
file_put_contents('/var/lib/postfix/message_user_map.json', json_encode($messageMap));
?>