How to interpret detailed error logs from Postfix or Exim?

Interpreting MTA logs requires understanding the format:

Postfix log structure:

Queue ID identifies message through processing. status=sent/deferred/bounced shows outcome. relay= shows destination server. dsn= shows enhanced status code.

Key Postfix patterns:

status=sent: Successful delivery. status=deferred: Temporary failure, will retry. status=bounced: Permanent failure.

Exim log structure:

Message ID tracks processing. <= incoming, => outgoing, asterisk-asterisk for failure. Detailed routing and delivery info.

Correlation approach:

Find queue/message ID for problematic message. Trace all log entries with that ID. Follow from receipt through delivery attempt. Extract final status and error.

MTA logs are the ship's detailed voyage record. Every decision and response is documented.