Contains the log file and temporary files associated with the messages in the mail queue.
The /var/spool/mqueue directory contains temporary files associated with the messages in the mail queue and may contain the log file. For further information, see the syslogd daemon.
Temporary files have names that
include the mail queue ID (MQID) of the message for which the file
|qfMQID||Queue control file|
|tfMQID||Temporary control file|
|xfMQID||Transcript file for session|
The /var/spool/mqueue directory is part of Base Operating System (BOS) Runtime.
The sendmail command.
The syslogd daemon.
Managing the Mail Queue Files and Directories in AIX 5L Version 5.1 System Management Guide: Communications and Networks.