I will, however contrast it from a system pont of view.* If you make it easy for the user to never have to go into their mailbox, they're less likely to go in there and clean things up.
That is, pardon my French, baloney.
I've heard of people here who allegedly keep more than 1000 messages in their inbox. That's part of why they added filtering on message content in Message Inbox (the person who added that, is one of those people).
This is not the way to force people to clean up. Instead, you to take harder measures, like putting a hard limit on the number of messages the system will hold, and automatically throw away older messages, when the inbox size grows above it.
Not that I really want this, but it surely sounds better to me, than what you are saying.
Is there a reason to limit the inbox size?