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Get more info:-Fix Microsoft Outlook not responding error
Make sure that Outlook is not in use by another process
Performance may be decreased if you use the Outlook AutoArchive feature or sync to Outlook with a mobile device. This is because these processes can use a large number of resources.
If Outlook is in use by another process, this information is displayed in the status bar at the bottom of the screen. If you try to perform other actions while Outlook is in use, Outlook may not respond. Let the task in process finish its job before you try another action.
Check the problem caused by external content
To resolve this issue, use one of the following methods:
Prevent Outlook to download external contents. To do this, go to File > Options > Trust Center > Automatic Download, select the following two options:
Don't download pictures or other content automatically in HTML e-mail option.
Warn me before downloading content when editing, forwarding, or replying e-mail.
Avoid sending such an email with external source.