Outlook Performance Series: Outlook 2007, POP3 & Windows Vista Issue – TCP Scaling

Welcome to troubleshooting performance issues - MS Outlook Performance Series - Part 5

Recently I was working with one of my customer, we came across a strange issue.

He has MS Outlook 2007 which was running on Windows Vista. He updated that it takes long time to download an e-mail message from a POP3 server in Microsoft Office Outlook 2007. Whenever they download a mail with attachment (for example .5 megabyte (MB) message), the download takes more than one hour.

Additionally, when they send e-mail messages by using the SMTP server of their Internet service provider (ISP), they get time out issue and also got the following error message:

Task 'Main - Sending and Receiving' reported error (0x800CCC0F) : 'The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP).'

At the end of the research, we found the issue happens due to "TCP Scaling", a new feature introduced in Windows Vista. This problem occurs if a network hardware device, such as a router, does not support TCP Window Scaling.

Please find the following article http://support.microsoft.com/kb/935400, which describes the issue and its resolution in-detail.

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