Disappearing E-mail

I’m running Exchange 5.5 and one of my clients is on 2000 Professional OS with Office 2000 Small Business. The problem is that there are e-mails not getting to her inbox. There are no similarities with these e-mails. Some have attachments, some do not, and they are from various senders. In exchange administrator under tools/track message the e-mails are there but they are not arriving to the account. I have tried MTA check, Isinteg, and Eseutil tools as well. I’ve reloaded Outlook 2000 and did all the updates. The only thing I haven’t done is blow out the e-mail account. This is an important account and I don’t want to risk losing anything, but I don’t know what’s left to do that I haven’t tried. Thanks for your help!