Mail loses messages

[Perry Hutchison]

Situation:  login, shell reports "you have mail."  Read mail (using
/usr/ucb/mail), enter "q".  The disk containing the mbox is full.  See
messages from kernel (write failed, file system is full).  Presumably
Mail got an error indication on the "write", but it went ahead and
cleared the incoming mailbox and reported "4 messages saved in mbox"
as if everything had worked properly.

Mail should *notice* that the write has failed, and preserve the incoming
mailbox.

This happened on SunOS 3.5 (derived from 4.2BSD).