Mail App OS X Icon - Alternative Great Britain version

To replace the Mail icon in Mac OS X 10.11 El Capitan you need to do the following:

- Restart your Mac in Recovery Mode by holding CMD+R at startup
- Go to Utilities > Terminal in the menu
- Type 'csrutil disable' and Enter
- Restart normally and change your Icon by showing the 'Get Info' windows and copying and pasting the icon.

To re-enable System Integrity Protection (SIP or Rootless)
enter csrutil enable by using the same method.