Lost Password for the newly created custom domain mail account

I registered the domain and setup the mail with outlook.

I created the user account and missed to note down the password.

I told the user about the new email address and not the password (bcoz I hav missed it)

I tried to login with ALL the possible combination i could recall but no vain. 

Delete and recreate the account is an option but the user is expecting some v important emails on the account (that he has not logged in once)

Is there any other solution for this ...