Mailbox Full though no such limit defined

Dear All,

I am facing following error at only one client's system.

Task 'Microsoft Exchange Server' reported error (0x8004060C) : 'The message store has reached its maximum size. To reduce the amount of data in this message store, select some items that no longer need, permanently (shift + del) delete them.'

Few things to tell you,

1. There is no such limit for the mailbox size on exchange server. So generally not a single user face such kind of issue, no need to create PST bcoz all the mails on server itself.

2. I have configured new laptop to the user, on earlier laptop there was no such issue occured.

3. Laptop config: XP service pack 2, office 2003, HP Probook

Kindly suggest.

Thanks & regards,
Sandeep