Poor Outlook performance and Nagle’s algorithm

I stumbled across a performance issue for Outlook, which was really not easy to troubleshoot:

Some users, migrated to Exchange 2013, reported very poor performance in Outlook. Switching between e-mails or folders was just horrible. Sometimes they even couldn’t connect to Exchange and they got an error like this:



But not all users experienced this issue. I also had to mention we started seeing this first on Terminal Servers, where cached mode was not available.

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How to block unwanted User Agent using F5

There are many ways to block applications based on User Agent. You can use ActiveSyncDeviceAccessRules for EAS or EWSAllowList/EWSBlockList.

Besides this you can block those User Agnets already on a load balancer. The main difference is that then the workload is moved away from you Exchange server to the load balancer. In this post I’m going to describe the steps of one possible way to do so taken a F5 load balancer.

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