"Temporarily" Blacklisted

Hi:

I have a Comcast email address, although I am no longer a Comcast customer, and keep getting a "Temporarily blacklisted IP address" error message. I run Linux Mint and Thunderbird as my email Client. I have had this problem, consistently, over the last year. It lasts for  a few days, and then it "magically" gets fixed. I have called Comcast support, and they tell me that as long as I can access their webmail version, that it's not a Comcast problem. I have called Cox Communications (my ISP), and they claim it's not their problem. I have turned off my modem for a few hours (so the IP address lease expires), and that sometimes solves the problem ( although I cannot reproduce this "solution" always). I regularly reset my modem/router every week. I know it's not a Linux/Thunderbird problem, as I started getting this problem when I was running Windows/Outlook. I currently have been "temporarily" blacklisted for a week this time, and I am reaching out for any other ideas on how to fix this problem. I have included output from the Thunderbird Error Console. Note the error claims my password failed, but I know I am entering the correct password. I am old-fashioned and want to continue to use POP3 - I do not need to use IMAP (unless it will solve this problem). Thanks for the help.