[topcat]

It seems my disk has one or more bad blocks. They seem to be in area where Mail has stored its Inbox (~/Library/Mail/account_name/INBOX.mbox). This has over 1000 messages and is over 80 MB in size. This first showed up when Mail tried to compact the mailbox - it failed with an error message that the disk might be full. It isn't - over 1.5 GB still free. Ran Norton Disk Doctor (ver 6.0.2), which fixed a couple of minor errors but always hangs when doing the media check. The manual says this could be the result of a bad block. Ran Disk Warrior verision 3. It also repaired a couple of minor errors, found no other problems, but the error persists. So how can I recover the data from the INBOX.mbox file? It has been possible to move messages one-by-one to a new mailbox but there are a lot of messages. Moving large blocks of messages causes Mail to crash.

Thanks for any help!

[malvolio]

I believe that running a defragmenting program will correct the problem by remapping your drive to avoid the bad blocks.
The safest defragger currently available is PlusOptimizer, which is included on the DiskWarrior 2.1 CD (no OS X version is yet available). Although this utility runs in OS 9, it works well on OS X disks. I have used it on my own OS X partition a couple of times.
Norton Speed Disk and Drive 10's defragger both leave you vulnerable to severe disk damage if anything goes wrong during the defragging process. PlusOptimizer does not.

[Cipher13]

If your drive is corrupted, don't defrag. Repair first.

Run DiskWarrior over the drive, that'll fix it.