How can I find my local mail spool?

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http://unix.stackexchange.com – I am a graduate student and a relative Linux novice. This question is a sort of spin-off of my earlier question. My institution has a Ubuntu Linux cluster. I am just a user; I do not have sysadmin permissions, and I certainly do not have the expertise to be a sysadmin! My question is, how do I find my local mail spool? As far as I know, I am not using a mail transfer agent. Answers to my previous question suggested that I look for a file /var/spool/mail/$USER, but unfortunately, I do not see a file corresponding to my user name. In /var/spool/mail/, using ls I only see two files: nobody (HowTos)