Weird Time Machine errors on Leopard Server

When I open the main GIU of the Leopard Server there's always an error pop up on the screen from Time Machine. This error states that 'a' backup malfunctioned, but all backups seem ok.

I looked through the logs and found this: (note that most backups finish ok, just some with the error below)
4/24/09 9:38:15 AM /System/Library/CoreServices/backupd[64124] Starting standard backup
4/24/09 9:38:15 AM /System/Library/CoreServices/backupd[64124] Backing up to: /Volumes/Time Machine Backups/Backups.backupdb
4/24/09 9:38:17 AM /System/Library/CoreServices/backupd[64124] No pre-backup thinning needed: 131.4 MB requested (including padding), 187.56 GB available
4/24/09 9:38:21 AM /System/Library/CoreServices/backupd[64124] Stopping backup.
4/24/09 9:38:21 AM /System/Library/CoreServices/backupd[64124] Error: (-43) SrcErr:NO Copying /private/var/imap/user/a to /Volumes/Time Machine Backups/Backups.backupdb/Saturn/2009-04-24-093816.inProgress/83D4516C-94ED-4201-9F20-9547F53209EF/Leopard Server/private/var/imap/user
4/24/09 9:38:21 AM /System/Library/CoreServices/backupd[64124] Copied 4 files (10.7 MB) from volume Leopard Server.
4/24/09 9:38:21 AM /System/Library/CoreServices/backupd[64124] Copy stage failed with error:11
4/24/09 9:38:27 AM /System/Library/CoreServices/backupd[64124] Backup failed with error: 11

I always thought that Time Machine does not backup mail stuff, but it apparently does backup parts (useless parts) of the IMAP mail store.

The fix I'm trying is to add the /var/imap/users/ dir to the exclude list in the Time Machine preferences screen. See if this helps....