Since upgrading to El Capitan yesterday, Mail has been a total nightmare to use. It started with it crashing every time I opened it until I found a tip to disable all the email accounts and then re-enable only one, let it download all emails, then repeat the process until all the accounts were enabled. That worked for about twenty-four hours. But now, I'm having a whole host of issues. Now whenever I open Mail, it slows my entire computer down to a crawl before everything just completely freezes. I've tried the disable/re-enable trick, but that doesn't work. I only managed to re-enable one account before my Mac completely froze up again.