Hi Bob,
Having made the move to a Mac I'd love to see if I can resolve the issue. I am sure it is not that complex, I am just not a master of the Mac! I am not sure what "system details" means, but I will provide all I can. So when I write an email using Apple/Mac email (via Yahoo exchange) the email page starts to flash. It goes back and forth between my specific email and and my email Inbox page. Eventually it sends, but this can take hours of flashing. I have had the Mac for a few years without mishap (I use a Windows machine at work) UNTIL I INSTALLED THE LATEST MAC OS HIGH SIERRA software. It start happening immediately after the update. I do not get an error message. My email client I think is Yahoo (I have a Yahoo email address), but I am using the Apple/Mac email program. My computer is a late 2013 15 inch Mac Pro with retina display. I am using the latest Mac software -- High Sierra 10.13.1. I am not using any third party apps to protect, clean, optimize or boost performance. Again, I think it is software related as everything was fine until I installed High Sierra 10.13.1 Any thoughts. Thanks for responding and offering to help. Much appreciated! Peter