I'm going Crazy with this email issue

Spent an hour with online chat.... thought we had it fixed......  I have done all the steps to update the security of my account.... now can't send emails!   My WEB email works just fine.... I know my log in name and password.... but the Windows live program and my phone email won't work.....  HELP  this is the error message.  Ever since I checked the required "server requires authentication" and it asks for my username and password.... which is correct as it works on webmail just fine to log on.... it just won't accept it!   Oh well, my hubby wants to dump Cox Internet and go with CenturyLink's great deal...  so it may not matter!

The message could not be sent because the server rejected the sender's email address. The sender's email address was '****e@cox.net'.

Subject 'Re: Tenant Registration Request for Rogers Ranch Unit 3 Homeowners Association Lot # 266'
Server Error: 550
Server Response: 550 5.1.0 Authentication required.
Server: 'smtp.cox.net'
Windows Live Mail Error ID: 0x800CCC78
Protocol: SMTP
Port: 465
Secure(SSL): Yes