Create an Outlook account with your Rackspace email account.
Choose the options of settings in Outlook.
Go to the Options, then go to the options of Connected Accounts portion of the Settings menu.
Then, under the Add a linked account feature, enter the options of other email account.
Enter the email address and password of Rackspace email account then enter the button of OK.
Then, choose the options of IMAP connection. Then chose the button of OK.
Read more here:- https://datarecovo.puzl.com/_news/How-To-Setup-My-Rackspace-On-Email-Clients%253F/298170
See Also this post:- https://www.bloglovin.com/@datarecovo/steps-to-log-in-appsrackspacecom-webmail-8395405