Should I be concerned?

Hello, For some reason (a post in another area while researching this http://discussions.apple.com/thread.jspa?threadID=1438597&tstart=0 issue prompted this), I was looking in /var/spool/imap and found a listing of folders that had names that match or partially match non-exsistant spam recipients on my server. Meaning names that keep showing up in the mail queue that are not actual users on the server. Here is the list from the folder: drwx------ 5 cyrusima mail 170 Feb 21 04:06 ^_-cyou drwx------ 5 cyrusima mail 170 Feb 21 01:48 ^_-e-link drwx------ 5 cyrusima mail 170 Feb 21 05:25 ^_-ericcrowder drwx------ 5 cyrusima mail 170 Aug 6 2007 ^_-gigbunchofgrahamsvus drwx------ 5 cyrusima mail 170 Mar 24 2007 ^_-kpbyv drwx------ 5 cyrusima mail 170 Feb 26 02:26 ^_-letbunchofgrahamsjig drwx------ 5 cyrusima mail 170 Sep 2 2007 ^_-liatyadai drwx------ 5 cyrusima mail 170 Jul 16 2007 ^_-mpachecaiju drwx------ 5 cyrusima mail 170 May 12 2007 ^_-mpachecal drwx------ 5 cyrusima mail 170 Jul 13 2007 ^_-mpachecape drwx------ 5 cyrusima mail 170 Jun 23 2007 ^_-mpachecaxgf drwx------ 5 cyrusima mail 170 Jul 3 2007 ^_-mpacheceiqqt drwx------ 5 cyrusima mail 170 Jun 23 2007 ^_-mpachecukg drwx------ 5 cyrusima mail 170 Feb 8 2007 ^_-vvf drwx------ 5 cyrusima mail 170 May 9 2007 ^_-zalapomuciamux drwxr-xr-x 2 cyrusima mail 68 Mar 12 07:23 stage. drwx------ 17 cyrusima mail 578 Nov 1 2006 user Most of the folders with the '^_-' in the name are spam recipients and not users... What does this mean?