If you need to run a cmdlet that changes one or more attribute of more than 1000 users you will receive an error if you try this following cmdlet:
Get-Mailbox | Set-Mailbox -RulesQuota:256KB
In this specific case we have to use ResultSize parameter in the Get-Mailbox cmdlet to list all your users and then they will be changed by the second cmdlet in the same pipe, as follows:
Get-Mailbox -ResultSize:5000 | Set-Mailbox -RulesQuota:256KB
Note: In this case my result size does not go over 5000 mailboxes. You have to change this value based in your number of mailbxes.
Note #2: There is also the value unlimited for the ResultSize switch which means that you can use -ResultSize unlimited and you don’t need to care to add a number higher than your current users because it will get all users no matter how many users you have.