What log files are available?
A qmail system is made up of several different programs, all running at the same time and doing their own little part of the overall "mail server" job. Each of these programs generally has its own log file, although if you are using syslog, the logs may be combined together. By understanding what each program does, you can easily tell which log file to look at when you need to check something.
The qmail-send program (which normally runs as a daemontools service called "qmail-send", or maybe just "qmail") manages the queue, and starts all delivery processes. The delivery programs run as children of qmail-queue, and therefore their output is contained with the qmail-queue output. If you have a problem with messages being "stuck" in the queue, this log file should be the place to look.
The qmail-smtpd program handles incoming SMTP traffic. If you have a problem with messages not being properly accepted or rejected from other machines, this log file should be the first place to look. Note that if you have multiple SMTP services on the machine (for example, a standard SMTP service on port 25, an SSL-enabled service on port 465, and an AUTH-only service on port 587) each service will have its own log file (again, unless they are being combined by the syslog mechanism.)
If you are using qmail-scanner as a way to have your incoming mail scanned for viruses and/or spam content, the qmail-scanner program also generates a log file of its own, which is totally separate from the qmail-smtpd log. You will find this file in your qmail-scanner directory, with the name qmail-queue.log. This will have a line-by-line description of everything the qmail-scanner program does.
If you are using simscan as a way to have your incoming mail scanned for viruses and/or spam content, you will normally find simscan’s logs in the qmail-smtpd service log.
If you are using clamav, the "clamd" program keeps its own log file. The /etc/clamd.conf file should have a "LogFile" line which tells you where the log is being written.
If you are using spamassassin, its "spamd" program also generates logs. By default it sends the logs to the syslog with the "mail" facility code, but by adding a "-s" option to spamd’s command line it is possible to send the log output to a file, or to the "standard error" channel (which makes it easy to run spamd under daemontools.) You should examine the command line for spamd in order to figure out where its log file will be found.
Any POP3 or IMAP servers will also be generating their own log entries. If you or your users are having a problem with POP3 or IMAP, those would be the place to look.
