just looked up the information on a Mail VS. This is from the VS R5.0 Manual.
1. If necessary, access the Programming Main Menu. If you are already at
the Programming Main Menu, skip to Step 2.
a. Press i777 or the programmed Voice Mail Auto Dial
button.
b. Press 99#.
c. Enter the password and press #.
d. Press 9.
The system plays the system programming options.
2. Press 4 for Mailboxes.
The system tells you how many mailboxes exist and how many are
allowed, then:
Please enter the mailbox number followed by # or
press # for the next mailbox.
3. Enter the number of a mailbox whose message length and size is to
change as indicated on Form 2, followed by #.
The system plays:
Mailbox XX exists. To administer the message length and
mailbox size, press 2. To reinitialize the password,
press 3. To reinitialize the mailbox, press 4. To
administer Outcalling, press 5. To program the Mailbox
Language, press 6. To administer Record-a-Call, press
7. To delete the mailbox, press *3. If finished with
this mailbox, press *#, or for the next mailbox, press
#.
4. Press 2 for Administer Message Length and Mailbox Size.
The system plays the message length and mailbox size.
5. Press 1 to confirm that you want to change the message length and
mailbox size.
6. Enter the message length (that is, a value of 2 to 60 minutes), followed by
#.
Note that this message length must be less than or equal to the mailbox
size that you enter in Step 7.
7. Enter the mailbox size (that is, a value of 5 to 180 minutes), followed by #.
Note that this mailbox size must be greater than or equal to the message
length that you entered in Step 6.
8. Press *# to accept the message length and mailbox size.
9. Repeat Steps 3 through 8 for each mailbox that you want to resize.
10. Press *7 to return to the Programming Main Menu.