Yea it's called a cloning program or important from a Time Machine back. Also if you have both connectioned up you could use /Applications/Utilities/Migration Assistant to import certain settings
Migration Assistant import all applications, you cannot choose only Apple Mail and Internet Account.
My scope is only to export these 2 objects and afterwards to reimport again in El Capitan in fresh installation.
Interesting link, but not helpful for this thread - which is not about settings, but about exporting mailboxes and internet accounts.
This is a relatively low traffic forum site, so relevant information is much better than just random stuff.