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Relevant Information:

OS: RedHat 9.0
Email: Qmail
HD: 120GB HD (basically sole purpose is just for email)
Courier-Imap server
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I have installed qmail and everything is working fine. The only problem is that I am getting email messages from qmail telling me that my mailbox is over 90% full and I need to clean it out. Where can I go to change the setting so that I basically have unlimitied space for email?

Space on the HD is not the problem for I have over 100GB still empty.

Can someone please help?

Depends... are you running vpopmail? Qmailadmin? If you're running both of these packages alongside qmail, you can change quotas very easily using a web interface. Very convenient!