You've got a cron job that's trying to run /sbin/service (part of the djb tcpserver tools I think), but it doesn't exist. You're getting mail since the command is generating output (if it was working, output would be directed to /dev/null).
Log in as root, and type
Remove the line(s) that contain the command (you'll be in the vi editor, so
will delete the entire line the cursor is on, etc), then do
to exit and save changes. No more cron job, no more emails.