Hi,
What type of email account are you using? Exchange, POP3, or IMAP?
Does this issue continue if we try to start Outlook in safe mode (outlook /safe)?
Do you have your email account configured on any other device, such as a mobile phone? If so, please try temporarily disable the synchronization and then see if this issue continues.
In addition, we may also try creating a new mail profile and then set up your email account in the new profile to see the result. For your convenience:
https://support.microsoft.com/en-us/help/829918/how-to-create-profile-and-set-up-an-e-mail-account-in-outlook
Regards,
Steve Fan
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