create logical volume (with cryptsetup binary):
# cryptsetup -y create maildir /dev/sda9

or create logical volume (with cryptsetup script which comes with hashalot package):
# cryptsetup -c aes -h ripemd160 -s 32 create maildir /dev/sda9

confirm it worked:
# dmsetup ls
maildir (254, 0)

create filesystem:
# mkfs.reiserfs /dev/mapper/maildir

mount filesystem:
# mount /dev/mapper/maildir /var/maildir