Can't send email with El Capitan

I have a MacBook Pro [circa 2011(12)] 13-inch, iOS 10.11, 500 gigabyte hard drive with plenty of memory left. Upgraded to Yosemite recently and outgoing email stopped working. Updated to El Capitan last night and outgoing email still not working. Email works fine on iPhone 6 and iPad3. I have tried deleting and resubmitting my email password, to no avail. Thoughts?