Can't create a new Mac Mail account in High Sierra...

Ten days ago my old Outlook for Mac 2011 just quit on me; couldn’t send or receive e-mails. Tried using Mac Mail with the same result. Called my ISP (Cox) and got a Tier 2 tech rep to look into it. They swear it’s nothing on their end. I’m currently able to log into Cox’s web mail, and am able to send & receive e-mails online. So I’m guessing there’s something wrong with my desktop (Mac mini).

I upgraded to High Sierra from Sierra (another nightmare, but I digress). Tried to set up my Mac Mail account, and just got to the window where it asks you to input your name, e-mail address, and e-mail account password. Tried it many times, and each time I got a spinning wheel that just kept going and going and going. After about 10 minutes of this I finally got a “couldn’t connect” notice (I don’t remember the exact language, but it was something to that effect). I tried deleting my old Mac Mail account and attempted to create a new one; got the same spinning wheel and connection failure. I tried setting up a new Mail account with a different User account: again failure. I tried resetting to my default Keychains and restarted: still unable to connect.

Then I downloaded three new e-mail apps: Spark, Spike and Thunderbird. Had the same failure with Spark and Thunderbird, but amazingly I was able to connect with Spike! For all three I was able to manually enter the server port settings, etc; at this point I’ve got them all memorized. Now I really don’t want to use Spike as my main e-mail program; I want to be able to use Mac Mail. Why would Spike connect when the other 3 failed?

I’m really hoping someone on this forum can help me out. Very frustrated! Also, is there anyway I can enter the server port settings manually on High Sierra when setting up a new account? I haven’t been able to find a way to circumvent the first dialog box that gets stuck on the spinning wheel (when setting up a new mail account).

Any advice, info, help will be greatly appreciated!