Some channel programs include optional code to assist in debugging by producing additional diagnostic output. Two channel keywords are provided to enable generation of this debugging output on a per-channel basis. The keywords are master_debug, which enables debugging output in master programs, and slave_debug, which enables debugging output in slave programs. Both types of debugging output are disabled by default, corresponding to nomaster_debug and noslave_debug.
When activated, debugging output ends up in the log file associated with the channel program. The location of the log file may vary from program to program. Log files are usually kept in the log directory. Master programs usually have log file names of the form x_master.log, where x is the name of the channel. Slave programs usually have log file names of the form x_slave.log.
On UNIX, when master_debug and slave_debug are enabled for the l channel, users then receive imta_sendmail.log-uniqueid files in their current directory (if they have write access to the directory; otherwise, the debug output goes to stdout.) containing MTA debug information.