XFOR: IMAP4 FETCH Command Returns Wrong Size

Microsoft Exchange Server returns the wrong message size in response to the IMAP4 command "FETCH RFC822.SIZE".

For performance reasons, Exchange Server defaults to returning an approximation of the message size. This can cause compatibility issues with some IMAP4 clients.

You can configure Exchange Server to return the exact message size by doing the following:

1. Start the Exchange Administrator program.
2. Select <Organization>, and then <Site>. Select Configuration, and then select the Protocols container.
3. Double-click the "IMAP4 (Mail) Site Defaults" object.
4. Clear the "Enable fast message retrieval" check box.

This setting can also be changed on a per-server basis, as follows:

1. Start the Exchange Administrator program.
2. Select <Organization>, and then <Site>. Select Configuration, select Servers, select <Server Name>, and click the Protocols container.
3. Double-click the "IMAP4 (Mail) Settings" object.
4. Clear the "Enable fast message retrieval" check box.

Changing this setting may decrease the overall performance of your Exchange Server information store while it is processing IMAP4 requests.

The following clients were tested and worked well with Exchange Server with the Enable Fast Message Retrieval option selected:

• Microsoft Outlook Express
• Microsoft Outlook version 8.5
• Netscape Messenger earlier than version 4.5
• Qualcomm Eudora Pro
• TeamWARE Embla 2.0
• CyrusSoft Mulberry 1.3.0
• Paladin Email 3.11
• Orangesoft Inc WinBiff 2.11

Other clients tested with the Enable Fast Message Retrieval option selected include:

• Pine versions 3.96 and 4.0. Result: With Pine 3.96, either message content is lost, or garbled text appears. PC Pine 4.0 stops responding on approximated sizes.
• ESYS Corp.s Simeon. Result: The client stops responding on approximated sizes, most notably messages containing embedded message attachments.
• Netscape Messenger 4.5. Result: Message content is lost because the client performs partial fetches up to the approximated size given by the server.
• Pine 4.04 displays the message: "Wrong message size. Continuing."

NOTE: The third-party products discussed here are manufactured by vendors independent of Microsoft; we make no warranty, implied or otherwise, regarding these products' performance or reliability.