Dear MOHAMMAD TAUQUEER ANSARI,
Thanks for using Microsoft products and posting in the forums!
From your description, I understand that you seem to be experiencing an inability to add an Outlook account in the iOS Mail app;
In order to better help you identify the problem, I need to gather the following information with you, thank you for your cooperation:
1, Did you get an error report while adding outlook account, can you provide some details screenshots?
2, What version of iOs do you have?
3, What protocol was used during the adding process (POP/IMAP/Outlook.com)?
In order to peel off the problem more quickly, I suggest you first go to webmail outlook.live.com through a browser, to check if you can login normally there. The purpose of doing this is to eliminate as many interruptions as possible, webmail synchronization is fast and good, so that you can easily figure out whether the problem is with the email account or with the Mail app for iOS.
If you can send and receive emails normally on webmail, it means that the problem is with Mail app; it is recommended that you update iOS to the latest version first, the update can often solve some unknown problems.
After updating the Mail app, re-add the Outlook email account to the Mail app, this step can focus on verifying the password issue, make sure you enter the correct password and configuration parameters, when adding an email account on phone, usually chooses outlook.com or IMAP.
Feel free to share more and let me know if you need any further assistance.
Best regards,
Harris-MSFT |Microsoft Community support specialist