Mail Can't Receive Email from One ISP

Yesterday morning upon returning to work, my Mail app was unable to receive emails from three accounts that are tied to the same ISP. (Other email accounts not related to this ISP receive mail successfully.) But on these three accounts, the little wheel next to the account name just spins and spins.

When I ran Mail Connection Doctor, I got the following report:

"Could not connect to this POP server. Check your network connection and that you entered the correct information in the Account preferences. Also verify that the server supports SSL. If it does not, deselect the "Use SSL" checkbox in the advanced tab of Account preferences."

My current settings have worked for years.

Now, when I flipped over to a different User Account on my Mac and recreated the mail account, I was able to successfully download my email. That tells me that my connection to my ISP not being blocked by IT here at work.

I've tried rebuilding the account. I've tried taking it offline and back online again. No success. Any suggestions on where to go from here?