Hypothesis: When you removed XAMMP, your computer's own hosts file wasn't updated, so the browser still thinks "localhosts" lives in the XAMMP directory-- which it can't find.

Disclaimer: I know nothing about XAMMP-- in fact I had to do a hasty edit when I found I'd been spelling it XAMPP-- but have always got MAMP to work more-or-less as intended. It's even possible to run multiple sites on the free version if you're prepared to get your hands dirty; you only have to do it once.

Do you know how to open your /hosts file in Terminal? Please say yes, because I don't have it internalized, and have to copy-and-paste my written instructions including finding where I wrote them down every time

Thanks lucy24

Seems to me nobody knows what is to be done here with my problem,so,
I am ready to try your idea about Terminal and learn something new for me.

Yes, I know how to open Terminal. Have seen many warning that it can damage my system if not used properly...it sounds scary to me.

I'll be very thankful if you send your step - by-step instructions from opening Terminal to closing it when the job is done!

I've just had a look at my own /hosts/ file and it doesn't say exactly what I thought it would.

But this will do no harm; you're just looking.

#1 find and open Terminal
At some point in what follows, you may be prompted for your computer's password. Generally it's triggered by the first occurrence of "sudo".

#2 at the prompt, type (with spaces as shown)
sudo cp /etc/hosts /etc/hosts.bak
(You are making a backup of the file "hosts" which lives in the invisible directory /etc/ which, on my system, is actually an alias of the similarly invisible /private/etc/. I use a quickie toggle called "Hidden Way"-- which I suppose I downloaded from somewhere-- to show and hide invisible files. They don't need to be visible; it's just educational to see everything that's there.)

#3 now type
sudo pico /etc/hosts
(You still haven't changed or edited anything. Now it is just showing you the content of the "hosts" file.)

See anything you don't expect? Mine says "localhost" twice: the first is the expected "127.0.0.1"; the second is "::1" which I would dearly like to have explained to me. Is it the IPv6 equivalent?

When done, just quit Terminal in the same way you'd quit any other application.

:: uneasily wondering how and why "mail.{my-www-host}.com" is listed in this file ::

Come to think of it, when did you last empty your browser cache? It would be embarrassing if it turned out your computer is blameless and it's the browser looking for something that isn't where it expected.