When analyzing qmail's operation for almost any purpose, the first place to begin looking is in qmail's log files. In a standard qmail setup, there are two sources of log files: one for qmail-send
and one for qmail-smtpd
. By default, these contain both useful information for tracking down individual messages and useful information for analyzing qmail's performance.
The log output of both qmail-send
and qmail-smtpd
is organized in a simple way, though it can easily become confusing.
The qmail-smtpd
log file is the simpler of the two because qmail-smtpd
does not generate log output. The qmail-smtpd
log records the output of tcpserver. tcpserver
generates five log entries for every connection:
1. When the connection opens, it logs the current number of connections and the maximum number of connections.
2. When the connection opens, it logs the client and the process-identifier (PID) of the child process handling that connection.
3. After all the necessary...