The outlook is configured to prompt for your credentials

When the User identification settings are enabled in Outlook (configured with an
Exchange account), it prompts continuously for login credentials. To get rid of
the password prompt problem, you need to disable this setting
How to disable this setting?
– Open your Outlook
– go to File >> Account Settings >> Account Settings


– Select the Exchange account and click the Change button

– Click More Settings in the new dialogue box.
– In the Security tab of Microsoft Exchange dialogue box, uncheck Always prompt for logon credentials