OS X El Capitan fix: can't send email after upgrade

**Update 21 Oct 2015: Apple released OS X 10.11.1 which claims to have fixed this problem**After upgrading many Macs to OS X 10.11 El Capitan, I'm finding a bug that seems to be quite consistent. Virtually everyone who uses an email address ending in @me.com is suddenly unable to send messages using the built-in Mac Mail program. Emails still come in but the outgoing messages don't go. Fortunately it's a very quick and easy fix.

1. Disable and re-enable your iCloud email.
   • Go to the Apple menu > System Preferences > iCloud (3rd row).
   • Click the checkbox next to Mail to disable it.
   • After waiting for the checkmark to disappear, click the box to turn Mail back on.
   • You can close the System Preferences window.
2. Set your outgoing email server.
   • Open Mail.
   • Click the "Mail" menu and choose "Preferences".
   • Switch to the "Accounts" tab.
   • Choose your iCloud account from the left column.
   • Look for "Outgoing Mail Server" on the right and switch it to "iCloud".
   • Close the Preferences window to return to Mail.

That should do it! If you have a lot of email in your iCloud account or a slow connection you may need to wait some time for your email to re-download, so don't worry if your email inbox is empty for a few minutes.