I have had webmin installed with the postfix module since before this happened.
No updates for at least a couple of weeks and have restarted since then.
Loads of space
df -h returns this
root@belle:/var/vmail/glemsfordschool.local# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 224G 5.8G 207G 3% /
tmpfs 993M 0 993M 0% /lib/init/rw
varrun 993M 380K 993M 1% /var/run
varlock 993M 0 993M 0% /var/lock
udev 993M 140K 993M 1% /dev
tmpfs 993M 0 993M 0% /dev/shm
lrm 993M 2.5M 991M 1% /lib/modules/2.6.28-17-server/volatile
So lots there.