Office desktop client users can face this issue due to several possible reasons when the outlook prompts for credentials frequently and it can be frustrating at times.
- When you open outlook and see need password prompt on the lower right corner.
- Close all office applications currently running on your desktop.
- Now go to Control panel > Credentials Manager > Windows Credentials
- Go to generic credentials tab and remove all the MicrosoftOffice16_Data
- Click on drop down arrow and then click Remove.
- You will get a prompt that if your " Are sure you want to permanently delete this Generic credentials ? ".Click on Yes. Do this for all MicrosoftOffice2016_Data.
- Now Open any of the office applications like Word or Excel and sign in to office application using your Work credentials.
- Enter your work/school email and credentials.
- Now open Outlook, you'll again get a prompt to enter your credentials and enter the credentials and do not forget to tick the checkmark "Remember my credentials" and click Ok
- Outlook gets connected to Microsoft Exchange and you no longer get the prompt to enter the credentials again.
Note: Taking Office 2016(Windows10) as reference, similar steps can be followed for other Office versions on different operating systems to stop this issue. This solves problem 9 out of 10 times but if this does not solve the problem then other troubleshooting steps needs to be performed.