Q: email addresses

I have a situation with my email accounts since I downloaded that last OS - El Capitan.  For a long time now I have used an @me email address with no problems whatsoever.  I was offered an @icloud address many years ago but have NEVER USED IT.  However, since the El Capitan, my computer has recorded/recognised I have an @icloud address and is showing it in my list of email accounts.  Why?  Also, I am constantly being requested to input a password for my @me and @icloud addresses.  I keep ignoring this request, and my @me email continues to be able to be received and sent without any problem.  Today, I thought I would go into my System Preferences and try and delete the @icloud account, but all attempts at trying to do this failed.  I even found out that to get into the @me account failed as a password was needed, - a password I didn't know I had, have no record of and even all my guesses failed.  Anybody experienced anything like this since El Cpitan?