We are using Exchange server 2003 with Outlook 2003 and 2007. Users are sometimes receiving winmail.dat attachments when sending email to each other,internally. These messages are internal, not going to the Internet. We have one domain, all users are members of the domain and are using Outlook connected to the corporate Exchange servers. I have noticed that this only happens when a user on Exchange serverA sends a message with an attachment to a user on Exchange server B, and the attachment is larger than 10MB. Again, both users are located in the same domain with mailboxes on different servers in the same domain, even located in the same office. If the message does not get transferred to one of the other mailbox servers, the user gets the intended attachment, not the winmail.dat. If I have the user turn Word off as the default editor, the recipientsget the intended attachment, not the winmail.dat?It seems that Micorosft is unable to decode its own message format. I am confused as to why this is happening internally with all users using Exchange/Outlook?Thanks

How about when you send email to external domain with an attachment of more then 10 MB?Have you tried after increasing the attachment limit on the server?Also check the message format on the exchange server http://support.microsoft.com/default.aspx/kb/821750Raj

Hi, Please check whether the Exchange Server has Trend Micro ScanMail installed. Based on my research, the issue may occur if some third-party software corrupted the message. If yes, I suggest you disable the software and check the issue again. ~~~~~~~~~~~~~~~~ Mike Shen TechNet Subscriber Support in forum If you have any feedback on our support, please contact tngfb@microsoft.com ~~~~~~~~~~~~~~~~