After installing the GM onto my 2009 macbook pro, running Mavericks, Mail will only send and receive mail if I've enabled "insecure authentication allowed" in Mail's preferences. IMAP & POP accounts both have the same problem. I then tried to reboot El Cap & I got a kernel panic on the opening screen. Obviously this keeps me from using El Cap. If I had been able to reboot back into El Cap & then been able to use mail without the risk of sending my password to my ISP insecurely, that would've allowed me to use El Cap securely and as I'm looking to purchase a new 27" Imac in the next couple of months for my business I'll have to seriously reconsider this purchase because of this problem. Anyone else seeing this or heard of it and what the fix might be? PS: UI is quite slow when using the trackpad to return to the last page visited in my browser. The shifting of the present page to the right to reveal the last page visited takes literally over a second. In Mavericks this "trick" doesn't exist and going back a page is pretty much seamless.