No, CloudMail mailboxes have a maximum size of 25GB and it cannot be adjusted up or down.
To check the size of a CloudMail mailbox, you'll need to log into the user's account at webmail.cloudmail.email. Once you're there, hover your pointer over the bar next to the disk icon to show the amount of space used.
There is currently not a way to globally view CloudMail mailbox sizes.
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