I ssh'ed into my server and found this email:

[admin admin]$ mail
Mail version 8.1 6/6/93. Type ? for help.
"/var/spool/mail/admin": 1 message
> 1 MAILER-DAEMON@dns3.a Wed Jun 5 08:50 13/568 "DON'T DELETE THIS MESSA"
& 1
Message 1:
From MAILER-DAEMON Wed Jun 5 08:50:27 2002
Date: 05 Jun 2002 08:50:27 -0700
From: Mail System Internal Data <MAILER-DAEMON@dns3.applelaptopbattery.com>
Subject: DON'T DELETE THIS MESSAGE -- FOLDER INTERNAL DATA
X-IMAP: 1023292184 0000000148

This text is part of the internal format of your mail folder, and is not a real message. It is created automatically by the mail system software. If deleted, important folder data will be lost, and it will be re-created with the data reset to initial values.

Do I need to be concerned?

Nope,
No need to concern. This is very normal for RAQ's, this email kind of message should stick in there as you can not be able to download it via POP3.

Just don't delete it using mail from the command line.

Its normal for that setup. Do as the message says - leave it alone.