After installing newer versions of the Receiver for Windows, that are by default configured to use only TLS 1.1 or 1.2, users are not able to add a store and may see this error message: "Your account cannot be added using this mail address. Make sure you entered it correctly. You may need to enter a server address."
https://support.citrix.com/article/CTX232266
https://www.citrix.com/content/dam/citrix/en_us/documents/products-solutions/citrix-receiver-feature-matrix.pdf