Can't send email

About a week ago (probably coincident with the April 24 Cox email security change), I have been unable to send emails from my Cox account using Outlook.  I created a new email account on Outlook, and have set it up per Cox instructions (POP, pop.cox.net, port 995 - smtp.cox.net, TLS, port 587).  The receive email function works, but it fails every time it tries to send an email.