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.

Subkey:

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

Entry:

TcpAckFrequency

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.

TcpAckFrequency.ps1
$strGUIDS=[array](Get-WmiObject win32_networkadapter -filter “netconnectionstatus = 2” | select -expand GUID)
foreach ($strGUID in $strGUIDS) {New-ItemProperty -path HKLM:\System\CurrentControlSet\services\Tcpip\Parameters\Interfaces\$strGUID -propertytype DWORD -name TcpAckFrequency -value 1}

Updated

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