In case you've ever wondered why your launchd scripts are not sending mail (even though they seem to be running), it's probably because of a silly incompativiliy between launchd and mail, described in more detail here.
To work around this, always include the following in your job's plist:
and then just reload the plist. I find myself doing that quite often, so this Bash alias helps cut down on typing:
alias lcreload="launchctl unload -w $1; launchctl load -w $1"