set up mail with optimum.net

I recently had to reinstall High Sierra on a replacement Mac Mini. All seems to work well after restoration from a Time Machine backup - except for Mail.

I have two Optimum email accounts. The original mail account, say "NAME@optimum.net" - is working perfectly on my Mac.

But I can not seem to set up the second account which Optimum calls an "Identity." Let's call it "ID@optimum.net." It will likely only receive emails from a single source: "source1@source.org."

I don't need or want a second password for that email account.

I have a Windows 7 PC, and it receives the mails for each, set up some time back, but because much of the settings are hidden by dots, or have different names, than the Mac settings, I can't use that info to set up the Mac mail. No matter what I seem to do, I get an "Unable to verify account name or password" error message when I click Save.

I cannot figure out what the incoming mail server or outgoing servers are - I believe both are "mail.optimum.net," what to enter for the Account, User name.

What is more puzzling, is that this identity apparently worked in the past, because I have many previously saved emails from this identity.

Any help would be appreciated.