Unable to reset my default keychains

If you had opened - system library - clicked on keychain - deleted all the files than system keychain will get corrupted , and you enter in user library - the first alfa numerical was deleted in older versions like Mac OS El - Capitan and previous ones .

This will remove passwords saved in it , when you again restart the Mac you have to save the passwords manually in internet accounts like web mail account and iCloud mail account also in air port express ( the wireless network or base station password ) > click on edit and enter the password .

But this method never works in Mac OS high Sierra .

Also login password is kept same as keychain password , and iCloud Keychain is totally different from it .

If Mac user has iCloud verification code in his records , the Apple ID , iCloud id and respective passwords , he can open keychain access through spotlight , open its preferences > click on reset my default key chain .

This will deactivate both your login keychain and icloud keychain .Follow the upcoming steps and enter new login password .

There are more methods by entering in recovery mode and resetting the login password , or creating a new keychain , but every time the most important of all " the iCloud verification code " that helps in every aspect must be in your records .

Try these methods , everyone is aware of reinstating the os , but that is not end of the world you can also take second opinion from apple support senior advisor ( they can ask to send log details ) and within a week the keychain can be reset see this link to contact them Contact - Official Apple Support

Contact Apple for support and service - Apple Support

For your Mail account problem

>System Preferences>Internet accounts> delete your email account from here, then go back to your Mail and add back your email account.

See this old thread login problems

Welcome !