I have Yahoo Mail accounts. These are free accounts. That means POP access is not allowed on those accounts. Normally a freebie Yahoo Mail user is stuck using the webmail interface to their account. However, they can use a local POP e-mail client to access the HTTP Yahoo Mail account by using the YahooPOPs POP-to-HTTP proxy. The POP e-mail client connects to YahooPOPs that then uses HTTP to connect to the Yahoo Mail account. I’ve also used SpamPal in the past. To get it to work on my Yahoo account meant chaining it through the YahooPOPs proxy. So my POP e-mail client would connect to SpamPal which then connected to YahooPOPs that connected to Yahoo Mail. Hotmail users can use FreePOPs to access their Hotmail account using an e-mail client that doesn’t support WebDAV or Deltasync protocols that Microsoft has employed. They use the POP e-mail client to (connect to SpamPal to) connect to to FreePOPs to connect to their Hotmail account. All this is possible because the proxies can be chained.
I see no means of handling CAS as a proxy so I can chain it in the proper position within that chain of proxies. I can’t see how to use CAS for a POP e-mail client that is using YahooPOPs to access their Yahoo Mail account via HTTP (and the same when using a POP e-mail client to use FreePOPs to access their Hotmail accounts via HTTP).