running out of disk space

I ran out of disk space this morning, and dmail broke the index files on 
several of my inboxes. Subsequent access with dmail or Pine gave 
"Oversize mix status record" and I had to repair the mailboxes, after 
deleting some junk and creating a new inbox so I would not lose any more
(ought to have got temporary failure and returned to local mail queue, 
but I'm not sure. Caught it relatively quickly)

Ideally, dmail should fail gracefully. I'm not sure quite how. Seeing if 
there's enough space to write the message, or double-buffering the index 
file maybe.

Fortunately this was all on my desktop, not the main mail server, 
otherwise I'd still be picking up the pieces tomorrow. Note to self - 
make quite sure we don't run out of space.