how to reinstall el capitan

• Hold cmd+r at bootup to get to Recovery Mode.
• OS X Utilties > Reinstall OS X

This will install 10.11 over itself without affecting your user files (so long as you don't choose "erase and install").

I had an issue with El Capitan beta 3 which prevented Mail working. I noticed that if I checked via "About" it did not even say El Capitan was the OS. I dexited therefore to reinstall adopting the method above. It reinstalls the original released version of El Capitan beta. You then have to upgrade through all the upgrades to get back to the latest. It put Mail right but I could no longer look at Photos. It kept telling me my version of Photos was not up to date. I logged a message back to Apple. This morning when I switched on I noticed that Beta 4 was there for me to update to. It was not yesterday. Doing that resolved the issue. I suspect though that being a beta version if anybody wants to reinstall he or she must be prepared to sit and go through each upgrade.

Other than this El Capitman seems OK. Parellels running Windows 10 also works fine.

A short follow up from my last post. Mail did work initially after the latest backup but that was short lived. It now continually crashes and will not open. The problem seemed to be a plug-in (GPG) which I have deleted.

When I got to the recovery disk, it said reinstalling was possible - I should use the application, which I don’t have. So, I tried to restore from backup but someone the formatting for the (RAID) partition was unforamtioned. How does one format this space so I can restore from my backup?