appendix ;-)
indeed, mount the disc under /var/vmail
(if your new disc is sdb with one partition)
edit /etc/fstab and add the line:
Code:
/dev/sdb1 /var/vmail ext3 defaults 0 0
then: mount /var/vmail
and now move the content of /var/vmail_old to /var/vmail
and you're good to go (no changes to ispconfig needed this way)