Log files (logs) are fundamental tools for diagnosing and resolving issues in IT infrastructure. One of the essential logs used in managing and diagnosing email services is maillog. This file contains records of all actions related to email services on the server, such as sending and receiving emails, user authentication, delivery errors, and more. In this article, we will explore how to read maillog and provide specific examples from practice to help identify and resolve common issues.
Basics of Reading Maillog
Maillog is usually located in /var/log/ on most Linux distributions, and its exact location may depend on the system configuration and the email server in use (e.g., Postfix, Sendmail, Exim). The file can be viewed using standard text manipulation tools such as cat, less, tail, grep, etc.
Format of Record
Each record in maillog typically includes the date and time, hostname of the server, service name (e.g., postfix/smtpd), process identifier (PID), and the message itself. The format of the message may vary depending on the type of event.
Example 1: Successful Email Delivery
Jan 12 10:23:45 mailserver postfix/smtp[12345]: 0A1B2C3D4E: to=<This email address is being protected from spambots. You need JavaScript enabled to view it.>, relay=example.com[192.0.2.1]:25, delay=0.35, delays=0.05/0.01/0.09/0.2, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as 123456789)
From this record, we can infer that the email with ID 0A1B2C3D4E was successfully sent to the address This email address is being protected from spambots. You need JavaScript enabled to view it. via the server example.com with IP address 192.0.2.1. The total delivery time was 0.35 seconds, with detailed breakdowns of delays in various stages. The status sent and code 250 2.0.0 Ok indicate successful delivery.
Example 2: Delivery Error
Jan 12 10:25:30 mailserver postfix/smtp[23456]: 1D2C3B4A5F: to=<This email address is being protected from spambots. You need JavaScript enabled to view it.>, relay=none, delay=0, delays=0/0/0/0, dsn=5.0.0, status=bounced (host example.com[192.0.2.2] said: 550 5.1.1 <This email address is being protected from spambots. You need JavaScript enabled to view it.>: Recipient address rejected: User unknown in virtual mailbox table)
This record shows that an attempt to send an email to the address This email address is being protected from spambots. You need JavaScript enabled to view it. failed because the recipient does not exist. The server example.com with IP 192.0.2.2 returned the error message 550 5.1.1 stating that the user is unknown. The status bounced indicates that the email was returned to the sender.
Problem Analysis
When analyzing maillog, it's essential to pay attention to status codes (DSN - Delivery Status Notification) and error messages, which provide crucial information about the nature of the problem. Using grep, you can efficiently filter records related to a specific email address, message ID, or particular error message.
Reading and analyzing maillog is a vital skill for any email server administrator. The ability to interpret records enables quick identification and resolution of problems, improves configuration, and ensures smooth operation of email services. We hope this article has provided you with a useful introduction to reading maillogs and helped you better understand common issues you may encounter.
