Compare the email address used in Exchange to your email address in Dynamics 365. If they do not match, update them so that they match.
If you are using Exchange Online, open the Office 365 Portal as an administrator and locate the user within the Users area. After selecting the user, click Edit next to the "User name / Email Aliases" section. Verify the Primary email address value matches the email address of the user record in Dynamics 365.
You can locate the user record in Dynamics 365 by accessing the Dynamics 365 application in your web browser and navigating to Settings, Security, and then clicking Users. The Primary Email value needs to match the primary email address in Exchange.
If you had to update the email address in Exchange, close and reopen Outlook before trying to access the Dynamcis 365 app. If you had to update the email address in Dynamics 365, you may need to click Approve Email within the user record.