how do /var/spool/(clientmqueue,mqueue,mail) work?

Question

If - for example - cron jobs output to stdout, which is the process collecting the output and writing to these directories ?

/var/spool/clientmqueue /var/spool/mqueue /var/spool/mail

Where can I find docs on the inner details (pipe, rpc, ...) of the "redirection" from stdout to mail files ?

If I send an email whith sendmail, does it do the same routing as above ? docs ?

Answer 1

I rename the sendmail true executable

/usr/sbin/sendmail

and replaced it with this bash script :

#!/bin/bash

LOGFILE=/var/log/sendmail_calledby.log
date >> $LOGFILE
cat /proc/$PPID/cmdline | tr '\0' ' ' >> $LOGFILE
echo >> $LOGFILE
echo $* >> $LOGFILE

The first fish caught in the net is CROND