Article ID: 909130 - View products that this article applies to.
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Important This article contains information about how to modify the registry. Make sure to back up the registry before you modify it. Make sure that you know how to restore the registry if a problem occurs. For more information about how to back up, restore, and modify the registry, click the following article number to view the article in the Microsoft Knowledge Base:
256986When a Post Office Protocol 3 (POP3) client tries to connect to a Microsoft Exchange Server computer that is behind a Microsoft Internet Security and Acceleration (ISA) Server firewall, the firewall may block the incoming POP3 connection.
(https://support.microsoft.com/kb/256986/ )Description of the Microsoft Windows registry
Note After several attempts, the client may succeed in connecting to the Exchange Server computer.
This issue occurs if all the available Winsock listening sockets that accept incoming POP3 connections are allocated by the ISA Server firewall for incoming POP3 connections.
Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.To resolve this issue , follow these steps:
If you still experience this issue after you follow these steps, increase the value of the ServerMappingBacklog registry entry.
To do this, follow these steps:
Article ID: 909130 - Last Review: January 15, 2015 - Revision: 1.3