I did what you suggested in your first reply removing the envelope files, but still have the problem...
As a result of your latest reply:
total 27928
drwxr-xr-x 26 502 20 - 884 23 May 23:27 .
drwxr-xr-x 13 502 20 - 442 23 May 22:58 ..
-rw-r--r--@ 1 502 20 - 12292 23 May 23:04 .DS_Store
com.apple.FinderInfo 32
-rw-r--r-- 1 502 20 - 1438 26 Aug 2012 .dat2c16.11c
-rw-r--r-- 1 502 20 - 16267 23 May 23:18 Accounts.plist
-rw-r--r--@ 1 502 20 - 32768 12 May 2012 AvailableFeeds
com.apple.metadata:FileSyncAgentExcludeItem 1
-rw-r--r-- 1 502 20 - 32768 23 May 23:16 AvailableFeeds-shm
-rw-r--r-- 1 502 20 - 321392 27 Sep 2012 AvailableFeeds-wal
-rw-r--r-- 1 502 20 - 10161 23 May 23:26 BackupTOC.plist
-rw-r--r-- 1 502 20 - 32966 23 May 22:51 DefaultCounts
-rw-r--r--@ 1 502 20 - 8278016 23 May 23:28 Envelope Index
com.apple.metadata:FileSyncAgentExcludeItem 1
-rw-r--r-- 1 502 20 - 32768 23 May 23:16 Envelope Index-shm
-rw-r--r-- 1 502 20 - 1957032 23 May 23:32 Envelope Index-wal
-rw-r--r-- 1 502 20 - 518 23 May 23:17 FlagMailboxes.plist
-rw-r--r-- 1 502 20 - 321096 7 Feb 11:19 LSMMap2
-rw-r--r-- 1 502 20 - 9428 10 Nov 2012 MessageRules.plist
-rw-r--r-- 1 502 20 - 9428 10 Nov 2012 MessageRules.plist.backup
-rw-r--r-- 1 502 20 - 811008 23 May 23:27 MessageUidsAlreadyDownloaded3
-rw-r--r-- 1 502 20 - 32768 23 May 23:17 MessageUidsAlreadyDownloaded3-shm
-rw-r--r-- 1 502 20 - 2261912 23 May 23:32 MessageUidsAlreadyDownloaded3-wal
-rw-r--r-- 1 502 20 - 76194 23 May 23:17 OpenedAttachments.plist
drwxr-xr-x 7 502 20 - 238 21 Mar 09:59 Signatures
-rw-r--r-- 1 502 20 - 309 23 May 23:17 SmartMailboxes.plist
-rw-r--r-- 1 502 20 - 309 21 May 22:19 SmartMailboxes.plist.backup
-rw-r--r-- 1 502 20 - 318 23 May 23:17 VersionedSmartMailboxes.plist
-rw-r--r-- 1 502 20 - 318 21 May 22:19 VersionedSmartMailboxes.plist.backup
thanks for your time, really appreciate it! Usually find help for random problems off the net and chat rooms fairly easily, but this appears to be an odd one:-(