Fixes OS X El Capitan Mail Problems
Another focused fix in the OS X 10.11.1 update is on the Mail app in OS X El Capitan. Users reported a number of issues soon after installing the update and it looks like Apple fixed a few of them with this upgrade.
Specifically Apple fixed a problem with server information and with displaying messages and mailboxes. Some users report that OS X 10.11.1 may have fixed a bug that automatically opened Mail when they turned on the computer, even with this option turned off.