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When you enable compression for Microsoft Office Outlook Web Access for Exchange Server 2003 in a mixed-mode Exchange environment, you may receive the following message:
Compression requires that all of your users accessing this virtual server have mailboxes that are on Microsoft Exchange 2003 back-end servers. See help with compression for more information.
Are you sure you want to enable compression? (Yes/No)
If you enable compression in a mixed-mode environment, Outlook Web Access clients may experience the following behaviors:
The Web browser window that displays the Outlook Web Access page does not have a scroll bar when the amount of text is larger than the window size. When this behavior occurs, the user cannot scroll down to view the whole window.
When a user replies to a message by using Outlook Web Access, the reply does not contain the message body from the message that the user is replying to.
This issue occurs when all the following conditions are true:
Your Exchange organization is configured in a mixed-mode environment.
The Exchange back-end server that hosts the user's mailbox is an Exchange 2000 computer.
The Exchange 2003 front-end server does not have Microsoft Exchange Server 2003 Service Pack 1 (SP1) installed.
To resolve this issue, install Exchange 2003 SP1 on your Exchange 2003 front-end server. For additional information about how to obtain and install Exchange 2003 SP1, click the following article number to view the article in the Microsoft Knowledge Base:
836993 How to obtain the latest service packs for Exchange Server 2003
For additional information about compression for Microsoft Office Outlook Web Access for Exchange Server 2003, click the following article number to view the article in the Microsoft Knowledge Base:
830827 How to manage Outlook Web Access features in Exchange Server 2003