Exim mail server, keeps a record of its activities in a hidden realm known as the "log". The first step in our log-reading journey is locating the Exim log, typically residing in the "/var/log/exim4/mainlog" chamber. However, it's always wise to consult your Exim configuration ("/etc/exim4/exim4.conf") for the exact location, just in case it's chosen a different hiding place.
Deciphering the Language:
Each entry in the log is a single line, a coded message composed of timestamps, IDs, addresses, actions, and sometimes, cryptic error messages. Don't panic! With a little understanding, these messages can be decoded:
Time: Each entry bears a timestamp, marking the moment of its creation. This helps you pinpoint specific events and track their timeline.
Exim ID: A unique identifier assigned to each message allows you to follow its journey through the Exim labyrinth.
Message ID: This unique identifier, like a fingerprint, distinguishes a specific message, even if it gets bounced around or relayed.
Sender/Recipient: These fields hold the addresses of the message's origin and destination, like clues leading to its birthplace and final resting place.
Action: This is the crux of the matter! Is the message delivered, bouncing back, or stuck in frozen limbo? The action field reveals its fate.
Errors: When things go awry, error messages appear, pointing out the roadblocks hindering delivery. Think of them as warning signs on the journey.
Unraveling the Mystery:
Now that you understand the language, it's time to analyze the log like a seasoned detective. Focus on timestamps for specific issues, use the Message-ID to track individual messages, and identify patterns linked to senders or recipients. The Action field is your key to understanding what happened to a message, while errors paint a picture of the obstacles it encountered.
Common Paths and Roadblocks:
Let's understanding the most common paths and roadblocks encountered in the Exim log :
Delivery Delights: started marks the beginning of a message's journey, while delivered signals its triumphant arrival.
Rejection and Bouncing: When things go south, failed indicates a delivery gone wrong, and bounced tells you the message has been sent back to its sender.
Connection Conundrums: Errors like connection refused or relay not permitted reveal difficulties reaching the recipient's server.
Authentication Agony: When passwords and keys don't align, authentication failed pops up, hinting at security hiccups.
User Enigma: If user unknown appears, it means the recipient's address doesn't exist, like a dead-end street on the delivery map.
To become a master log-reader, equip yourself with some handy tools:
Filters: Tools like grep let you focus on specific keywords in the log, streamlining your investigation.
Analyzers: Specialized Exim log analyzers can visualize and parse the log entries, making them easier to digest.
Documentation: The Exim documentation is your ultimate guide, offering detailed explanations of the log format and troubleshooting tips.
Remember: the Exim log is a valuable resource, providing insights into your email server's health and performance. With the right approach and a bit of practice, you can confidently navigate its cryptic messages and uncover the secrets hiding within. So, put on your detective hat, grab your trusty tools, and embark on your journey into the fascinating world of Exim logs!
These lines can readily be picked out by the distinctive two-character flags that immediately follow the timestamp.
Let us understand the symbols:
Below are the symbols which are used in the log:
1. <= This is for message arrival
2. -> This is for additional address in same delivery
3. *> This is for delivery suppressed by -N
4. ** This is for delievry dailed or address bounced
5. == This is for delivery deferred; temporary problem.
6. (= This is for message fakereject
7. => This is for normal message delivery
8. >> This is for cuttthrough message delivery
Summary of Fields in Log lines:
Check out this table to see what each piece of information stands for:
| Column | Description |
|---|---|
| A | Authenticator name (optional id and sender) |
| C | SMTP confirmation on delivery |
| Ci | Connection identifier |
| CV | Certificate verification status |
| DKIM | Domain verified in incoming message |
| DN | Distinguished name from peer certificate |
| DS | DNSSEC secured lookups |
| DT | Time taken for delivery (or attempt) |
| F | Sender address (on delivery lines) |
| H | Host name and IP address |
| I | Local interface used |
| id | Message ID (from header) for incoming message |
| K | CHUNKING extension used |
| L | PIPELINING extension used |
| M8S | 8BITMIME status for incoming message |
| P | Protocol used (on <= lines) or return path (on => and ** lines) |
| PRDR | PRDR extension used |
| PRX | Proxy address |
| Q | Alternate queue name |
| QT | Time spent on queue |
| R | Reference for local bounce (on <= lines) or router name (on => >> ** and == lines) |
| RT | Time taken for reception |
| S | Size of message in bytes |
| SNI | Server name indication from TLS client hello |
| ST | Shadow transport name |
| T | Message subject (on <= lines) or transport name (on => ** and == lines) |
| TFO | TCP Fast Open used |
| U | Local user or RFC 1413 identity |
| X | TLS cipher suite |
Remember: the Exim log is a valuable resource, providing insights into your email server's health and performance. With the right approach and a bit of practice, you can confidently navigate its cryptic messages and uncover the secrets hiding within. So, put on your detective hat, grab your trusty tools, and embark on your journey into the fascinating world of Exim logs!
