Unfortunately I'm not sure if this is directly tied to my El Capitan upgrade: My wife and I each have .mac accounts on our shared MacBook Pro Mail application. Yesterday morning everything was fine but when we opened Mail yesterday afternoon her account was gone. I went into accounts expecting to see that the 'enable this account' box was unchecked but that isn't the case. The account is just gone as if it had never been there. i tried to add it but after selecting that it's an iCloud account and entering the account name and password, the set up screen disappears and I'm left looking at the account list as it was. Her mail still shows up on her phone and our iPad. Ideas???