MS Outlook/Exchange Server Problem Sending eMail

[nbv]

I recently installed MS Exchange Server 5.5 at our office. We use MS Outlook 2000 as our eMail program. I thought everything was working fine until an employee pointed out to me that when we try to send an email to two or more people, MS Outlook automatically deletes the first email address in the "To" field. This only happens sometimes though. Other times, when the first email address isn't deleted, I receive an email back saying "Undeliverable" from the System Administrator. I cannot figure out why this is happening. It is very strange, and the first time I have heard of something like this. Any help would be greatly appreciated.