How to Investigate Email Spam/Abuse Problems in CentOS/AlmaLinux 8.7 on a DomainIndia VPS
As a server administrator, dealing with email spam and abuse issues is a common challenge. This article will guide you through the process of investigating email spam and abuse problems on a CentOS/AlmaLinux 8.7 VPS from DomainIndia, using Exim as the email server. We will cover searching logs using client domains, email IDs, Exim message IDs, authentication details, and more.
Table of Contents
- Accessing the Server
- Locating Exim Log Files
- Searching Logs Using Client Domain or Email ID
- Searching Logs Using Exim Message ID
- Analyzing Authentication Details
- Examining Message IDs and Other Information
- Taking Action and Securing Your Server
Accessing the Server
The first step in the investigation process is to access your server. You can do this by logging in to your CentOS/AlmaLinux 8.7 VPS using an SSH client like PuTTY or Terminal, with your root or sudo user credentials.
Locating Exim Log Files
Exim log files are essential for investigating email issues. The default locations for Exim log files on a CentOS/AlmaLinux 8.7 server are:
Searching Logs Using Client Domain or Email ID
To search for log entries related to a specific client domain or email address, use the
grep command. For example, to search for all log entries related to "example.com" domain, run:
grep "example.com" /var/log/exim_mainlog
Replace "example.com" with the client domain or email address you want to investigate.
Searching Logs Using Exim Message ID
If you have an Exim message ID, you can search for log entries related to that specific email. Use the
grep command with the Exim message ID as the search parameter:
grep "1pxVwq-00***U1-0Q" /var/log/exim_mainlog
Replace "1pxVwq-00***U1-0Q" with the Exim message ID you want to investigate.
If you want to examine the Exim rejectlog as well, you can run the following command:
grep "1pxVwq-00***U1-0Q" /var/log/exim_rejectlog
To save the output to a separate file for easier analysis, you can use the following command:
grep "1pxVwq-00E4U1-0Q" /var/log/exim_mainlog > output.txt
This command will save the matching log entries to a file named
output.txt in the current directory.
Open the output file with a text editor like
vi to analyze the log entries:
Based on the Sample log entry, here's a detailed breakdown of the information:
Date and Time: 2023-05-01 22:18:48 - This is the timestamp when the email was sent.
Exim Message ID: *pxV*-0**1-0Q - This is the internal Exim message ID for the email.
Sender: firstname.lastname@example.org - This is the email address of the sender.
Hostname: H=(ADMIN) - This indicates that the email was sent from a host identifying itself as "ADMIN".
IP address and port: [1*5.1*5.2*2.251]:63482 - This is the IP address and port number from which the email was sent.
Protocol: P=esmtpsa - This indicates that the email was sent using the ESMTP (Extended Simple Mail Transfer Protocol) with SMTP authentication.
Encryption: X=TLS1.2:ECDHE-RSA-AES256-GCM-SHA384:256 - This shows that the email was sent using TLS 1.2 encryption with the specified cipher suite.
Authentication: A=dovecot_plain:email@example.com - This indicates that the email was authenticated using the Dovecot_plain authentication method with the specified email address.
Email Size: S=7579 - This is the size of the email in bytes.
Message-ID: id=1****XJU4.A****Y2OA2@example.com - This is the message ID you were initially looking for.
Subject: T="Exodus - Account accessed" - This is the subject of the email.
Recipient: for m**.hoef*****gr@g****x.com - This is the email address of the recipient.
Based on this log entry, you can see that the email was sent from the "firstname.lastname@example.org" email address, using the "18.104.22.168" IP address. The email was authenticated and encrypted, indicating it was likely sent from an authorized user.
To investigate further, you can:
Check if the "email@example.com" email account has been compromised. If necessary, reset the account password and review account activity.
Perform a reverse IP lookup on the "1*5.1*5.2*2.251" IP address to identify the location and owner of the IP address.
Look for other log entries with the same sender, IP address, or message ID to gather more information and determine if this is an isolated incident or part of a larger issue.
Analyzing Authentication Details
Authentication details in log entries can provide valuable information about the sender's email account and authentication method. Look for log entries containing the
A= field, which indicates the authentication method used. For example:
This log entry shows that the email was authenticated using the Dovecot_plain authentication method with the specified email address.
Examining Message IDs and Other Information
While investigating email issues, you may need to examine other information, such as Message-IDs, timestamps, sender and recipient email addresses, IP addresses, encryption methods, and more. Use the information from the log entries to identify patterns, unauthorized access, or compromised accounts.
Taking Action and Securing Your Server
Once you have identified the source of the spam or abuse issue, take appropriate action to secure your server and prevent future incidents. Actions may include:
- Resetting passwords for compromised email accounts
- Implementing stricter authentication methods
- Blocking malicious IP addresses
- Configuring spam filtering tools
- Enforcing rate limits for outgoing emails
- Monitoring server logs regularly for suspicious activity
Investigating email spam and abuse problems on a CentOS/AlmaLinux 8.7 VPS from DomainIndia requires a systematic approach to search and analyze Exim log files. By using the appropriate search parameters, such as client domains, email IDs, Exim message IDs, and authentication details, server administrators can identify the sources of email issues and take appropriate action to secure their servers. Regular monitoring and maintenance of email servers are essential to ensure a secure and reliable email service for your users.