Outlook slow after migrating to Exchange 2013

Outlook can be slow in Online modus sometimes when you move mailboxes to Exchange 2013. I seems that Windows 7 with Outlook 2007/2010 & 2013 sometimes have some issues.

Before applying this TCP Ack solution, the below conditions must be met:

– OWA connection and mail browsing is very fine, whereas an Outlook online mode (i.e. not cached mode) connectivity is quite sluggish when mailboxes are on Exchange 2013…

– If OWA is slow as well, then the issue may be a general network slowness issue – check the network latency using Ping

– On Outlook Connection Status dialog box (CTRL+Right Click the Outlook icon on the Windows notifications part of the taskbar), Avg. Proc. time is fine, below 50~60ms, and Avg. Resp. time is over 110ms.

More information about the TcpAckFrequency registry key:

Quoting from http://support2.microsoft.com/kb/328890

– TcpAckFrequency is a registry entry that determines the number of TCP acknowledgments (ACKs) that will be outstanding before the delayed ACK timer is ignored.

– TCP uses delayed acknowledgments to reduce the number of packets that are sent on the media (Wifi, Wire,…)

– As data is received by TCP on a particular connection, it sends an acknowledgment back only if one of the following conditions is true:

  • No acknowledgment was sent for the previous segment received.
  • A segment is received, but no other segment arrives within 200 milliseconds for that connection.

Typically, an acknowledgment is sent for every other TCP segment that is received on a connection unless the delayed ACK timer (200 milliseconds) expires.

– You can adjust the delayed ACK timer by editing the following registry entry.


HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\<Interface GUID>



Value Type: REG_DWORD, number
Valid Range: 0-255
Default: 2
Description: Specifies the number of ACKs that will be outstanding before the delayed ACK timer is ignored. Microsoft does not recommend changing the default value without careful study of the environment.

$strGUIDS=[array](Get-WmiObject win32_networkadapter -filter “netconnectionstatus = 2” | select -expand GUID)
foreach ($strGUID in $strGUIDS) {New-ItemProperty -path HKLM:\System\CurrentControlSet\services\Tcpip\Parameters\Interfaces\$strGUID -propertytype DWORD -name TcpAckFrequency -value 1}


KB2888049 Update is available that improves the network performance of Internet Explorer 11 in Windows

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