Last updated: December 4, 2019

​​Is Outlook running really slow on your Windows PC after your mailbox is converted to Office 365? This can be resolved in most cases by the following procedure:

1. From within Outlook, select File > Account Settings.

2. Ensure you email account is selected, and then click Change...

3. In the Offline Settings section, ensure that Use Cached Exchange Mode is enabled. You can set the "Mail to keep offline" as needed (recommended value is 12 months). 

4. Select Next and Finish to save these settings. 

You will be prompted to restart Outlook, which is required for this setting to take effect. 

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Having trouble? We can help.​

Enabling the offline cached mode as described above should resolve a sluggish and slow Outlook experience after mailbox migration to Office 365. However, keep the following in mind:

• This procedure only applies to Outlook running on a Windows PC. Outlook on Macs have this setting by default.
• When this setting is enabled, Outlook creates a local offline file to sync mail to. After performing the above procedure and restarting Outlook, the file is built for the first time and depending on the size of your mailbox Outlook may be a little slow for the first few minutes during the initial sync. After the file is built, however, Outlook will perform as expected.
  
• During the offline file building process, searching for mail may also be slow. 
  
• ​Lastly, depending on the size of your mailbox, your local PC may not have enough drive space to store the offline file. This will require a ​technology support services ticket to resolve. 
  

Need more help? Please contact the Help Desk.

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