Entourage & Exchange sending duplicate e-mails

[Cyberkiller]

We have an Entourage client connected too our exchange server. Sometimes when the user sends an e-mail out to (outlook users) we receive the e-mail twice or sometimes even three times when the user only sent it once. Is there any known fix for this behavior? Also sometimes it will send out very old e-mails or random e-mails.

Thanks.