Based on my research, I have found some threads discussed similar problems. Please try the following methods and check the result.
1. Please have Outlook to work in offline mode by clicking Work Offline
button to check the result. The Work Offline button is under the
Send/Receive tab. The method is discussed in the following thread:
2. Try to change the Exchange proxy authentication settings from basic to NTLM. The setting can be found here: File > Account Settings > Account Settings > Highlight your Exchange account and click
Change > More Settings > Connection > Exchange Proxy Settings > Proxy authentication settings…
Microsoft is conducting an online survey to understand your opinion of the Technet Web site. If you choose to participate, the online survey will be presented to you when you leave the Technet Web site.