Setting up Mail with my ISP; logon issues.
My isp's mail does not recognize my password. I deleted both iCloud and the prior attempt, to try to start again. The server, of course, knows nothing of Macs, or it's Mail.
Mac mini, macOS 10.15
You ISP should have directions on how to set it up, even if you have to do it manually. I would call them or use another email address like Gmail, Outlook etc, etc to get the help.