I've got over 5000 in mine - so what?
The nature of the business that the company does is such that a contract can be up to a decade from inception to completion. Emails are part of legal business, so have to be kept. The Exchange server is backed up, archives on hard drives are not, and are subject to corruption.
ICT is there to serve the business, not to impose limits that restrict what the business can do. If there is a business case for increasing the current 1GB limit on email, then ICT will make it happen. A helpdesk tech will visit to let the user know that the size has been increased, and ask if there is anything else ICT can do.
Educating users is fine - we have some great how-to documents internally on-line, including how to manage mailbox size - but don't go placing restrictions on the people who make the money that pays for your support function.
ICT Support has a lot of power in the business. It has the power to empower the users who are engaged in company business to be more effective, and it has the power to control them. These two powers tend to be mutually exclusive, so the question is: which one do you think gives better job security?