Go to options of settings.
Enter the first and last name.
Enter your Rackspace email address.
Set the password for your email address to be the same as the password for your computer
Choose the options of SMTP Server from the options of drop-down menu.
“secure.emailsrvr.com” is the outgoing mail server.
Enter server Port Number: 465
Requirement of Authentication- Yes
Select SSL/TLS to: No
Enter the button of save for the Rackspace email settings in SMTP.
See Also this Post:- https://www.datarecovo.com/apps-rackspace-webmail-login/