How to optimize Microsoft 365 application performance

Table of Contents

Case #

You observe performance delays or freezes/crashes in any of the Microsoft 365 applications, including the Microsoft Outlook client. This how-to article provides guidance on how to optimize Microsoft 365 application performance.

Solution #

Carry out the following steps to optimize Microsoft 365 application performance:

  • Ensure that you have a healthy Microsoft 365 Apps installation, whether that be on Windows, MacOSX or a mobile device (iOS or Android).
  • Optimize the file size limit for all your .ost and .pst files in Outlook by following instructions at
  • Run the mailbox cleanup and compact tools for all your .pst and .ost files by following instructions at
  • Check that your Outlook setup does not break the software performance limitations and take appropriate remediation actions, if needed, as per the following article:
  • If you have a VDI solution with hybrid profiles, such as FsLogix or Citrix Profile Management, you should consult with the profile solution vendor for a profile shrink or profile compact script which should be run periodically to keep the overall disk size of the profile relatively low and always within set boundaries. This should be combined with any other potential policies (e.g. Group Policy) which define the maximum profile file size of a container-based solution, such as FsLogix (profile container and O365 container). Periodically cleaning up profiles is also a good idea in most cases.
  • Ensure you configure your Windows local group policy or domain group policy to set a proper size for the Outlook Cached Exchange Mode setting. This should be set to 1 or 3 months or higher if your end users require it for specific reasons. This setting should eliminate the overall profile size and thus avoid cases of email profile bloat or profile corruption.
  • If you are using an Exchange Online mailbox which comes with Online Archiving, make use of the Online Archive Mailbox to periodically move old and unneeded emails from the primary mailbox to the online archive mailbox, thus reducing the overall size of the primary mailbox.
  • Ensure that you remove as many Microsoft 365 App add-ons as possible, as it is a fact that many add-ons coming from third party providers significantly increase Microsoft App load times and contribute to slow starts and application crashes.
  • Beware of the impact which your local machine or VDI machine hardware specifications might have on the overall Microsoft client performance, especially in cases where you make heavy usage of the application, for example when using multiple mailbox accounts and data files (pst) simultaneously on the same Outlook client. Ensure you review the system requirements for your version of Microsoft Office apps. Check the disk health and run a defragmentation of the disk where the Microsoft Apps are installed and carry out periodic hardware and software maintenance to ensure optimal performance.
  • Test your IP network connectivity to the Internet and to the Microsoft 365 services by utilizing the Microsoft Office Connectivity tool available at This tool allows for a network connectivity test providing detailed results about network latency and other metrics such as RTT. It also allows for checking the Microsoft 365 (including Exchange Online servers) health status in a global map in real time.

Remember that you can always make use of the online versions of your Microsoft 365 Apps (Office Online), such as for example the Outlook on the Web (OWA) client, while you are investigating performance issues in your Microsoft Outlook client installation.

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