Kyocera KM-1500 Command Reference Manual page 366

PRESCRIBE Command Reference
Files
356
To set 9999 as the password for virtual mailbox number 3 for
which no password is set:
!R! VMPW 3, 0, 9999; EXIT;
To set no password for the virtual mailbox with the alias
MyMailbox for which the password 9999 had been set:
!R! VMPW "MyMailbox", 9999, 0; EXIT;
To change the password for the virtual mailbox with the alias Purchase Dept. from 9999
to 3333:
!R! VMPW "Purchase Dept.", 9999, 3333; EXIT;