By default, Virtualmin will store domain and mailbox passwords in various hash formats so that the password is available when adding new features to the domain. However, not all hash formats are equally secure, so this field can be used to disable storage of some formats. Regardless of what you select here, the password will always be stored hashed using the system's default format in `/etc/shadow` or LDAP though.

Be aware that disabling the MySQL hash format may prevent Virtualmin from creating a MySQL login for mailbox users with the same password that the mailbox was originally assigned. Disabling the Web digest format may prevent access to a protected web directory by mailbox users.