I'm not sure if this is a coincidence or not but after updating to the latest virtualmin this morning my mail delivery stopped. Looking in the maillog I saw the following message..
status=bounced (Command died with status 127: "/usr/bin/procmail-wrapper -o -a $DOMAIN -d $LOGNAME". Command output: sh: /usr/bin/procmail-wrapper: No such file or directory )
Running 'locate' showed the file to be in /usr/bin/ but doing a 'ls' in /usr/bin/ showed it was no longer there.
I found a copy of procmail-wrapper in /usr/libexec/webmin/virtual-server/ so I copied it from there to /usr/bin and I started getting mail again.
I'm assuming that procmail-wrapper is webmin specific. Has anyone else had theirs go missing?